President Obama and his Republican challenger, former Massachusetts Gov. Mitt Romney, engaged Thursday night in a sometimes spirited, but always cordial, debate that got very technical at times.

It was the "corporate executive" (Romney) vs. the "government professor" (Obama) and the GOP nominee appeared to be "full of confidence and full of sales pitch," NPR Senior Washington Editor Ron Elving says, while Obama put pressure on the Republican to explain what he would do as president.

There were few memorable lines — Romney at one point labeled Obama's policies "trickle down government" and Obama said Romney's plans for tax cuts would leave average Americans "picking up the tab." But overall, it wasn't an affair full of "zingers." Instead, the two contenders tossed around numbers — Obama said Romney would cut taxes for the wealthy by $5 trillion and Romney said Obama would cut Medicare funding by $716 billion — that they each disputed.

Will the debate at the University of Denver, the first of three in coming weeks, change the dynamics of what appears to be a very tight battle for the White House?

NPR national political correspondent Mara Liasson said afterward that as of this evening, there wasn't any reason to think the debate would change the race. But that could change in coming days as pundits weigh in and as video clips start circulating.

We live blogged as they debated at the University of Denver. The moderator was Jim Lehrer of the PBS NewsHour.

Update at 10:35 p.m. ET. In Closing, Two Different "Paths":

Obama, as determined beforehand, gave the first closing statement. He ran through some of the things accomplished the last four years, including the end of the war in Iraq and the killing of Osama bin Laden. And he said that among the promises he made four years ago was that he "wouldn't be a perfect president ... but would fight every day" to do what's right. "I've kept that promise," he said, and promised to do so again if he's re-elected.

Romney said he and the president would take the nation on "two paths that lead in very different directions." And if you look at Obama's record, Romney said, the path the president would take the nation would likely lead to weak job growth, cuts in Medicare and "dramatic cuts to our millitary."

Update at 10:25 p.m. ET. Romney Says Federal Government Has Role To Play In Education; Obama Says "Budgets Matter"; Romney Raps Obama's Priorities:

The Republican nominee says he agrees with some of the things the Obama administration has been doing on education. Obama responds that Romney's tax cuts for "folks like me and him" would force a 20 percent cut in federal education spending. To which Romney says he would not cut education funding and criticizes the Obama administration for putting "$90 billion into green jobs. That would have hired 2 million teachers."

Update at 10:15 p.m. ET. Romney Cites Reagan As A Model For How To Govern:

Obama says Romney isn't giving Americans enough details about the policies he would pursue. Romney responds that "my experience as a governor is that if I come in and lay down a piece of legislation and say 'it's my way or the highway,' " not much gets done. He would emulate Ronald Reagan, who "laid out his principles" and then worked with Congress.

Update at 10:10 p.m. ET. Romney Pushes To Repeal "Obamacare"; Obama Says It Was Modeled After Romney's Effort In Massachusetts:

After Romney makes his case for why "Obamacare" should be repealed — focusing on what he says are too-high costs and an "unelected board that's going to tell people ultimately what kind of treatments they can have" — Obama says "we've seen this model work really well, in Massachusetts, because Gov. Romney did a good thing working with Democrats in the state."

Romney responds that Obama didn't work across party lines, but instead came up with a plan "that you and Nancy Pelosi and Harry Reid thought was the best idea."

To which Obama says that his plan originally was bipartisan, but it was Republicans in Congress who chose to not work with his administration. "Democrats in Massachusetts might have given Republicans in Congress some advice on how to cooperate," Obama says.

The president also disputes the charge that an unelected board will tell people what treatments they can have. It will be "health care experts" trying to "figure out how we can reduce the cost of health care," he says.

"This board ... can't make decisions about what treatments are given," Obama adds. "It's prohibited in this law."

Update at 9:55 p.m. ET. Sharp Differences On Medicare Policies:

Obama begins a discussion of entitlements by talking of his grandmother, who was able to remain independent at the end of her life because, he says, "of Social Security and Medicare."

Romney, looking to reassure seniors that he wouldn't do anything to affect them, says "neither the president nor I are proposing any changes for current retirees." But Obama, Romney says in a repeat of things he's said many times before, would reduce benefits for future retirees by "cutting $716 billion from the program."

Obama, who has previously said his cuts would not affect retirees, counters that the "voucher plan" favored by GOP vice presidential nominee Rep. Paul Ryan would "cost the average senior about $6,000 a year."

PolitiFact has previously said the charge that Obama would "funnel" $716 billion out of Medicare at the expense of the elderly is "mostly false." The charge that Ryan's plan would raise costs for Medicare beneficiaries by $6,000 each is "half true," PolitiFact says.

Update at 9:40 p.m. ET. Romney Points To Broken Pledges; Obama Talks Of Being Balanced:

Romney takes the president to task for promising to cut the budget deficit in half, but instead being in the Oval Office as annual deficits grew to more than $1 trillion. Obama, meanwhile, faults Romney for saying during the GOP primaries that he wouldn't accept $1 in higher taxes in exchange for $10 worth of spending cuts. There has to be a balance between raising revenue and cutting spending, the president says. Romney responds that "you'll never balance the budget by raising taxes." The way to do it, he says, is to reduce tax rates so that job growth resumes and more people are paying taxes.

After the president says that some corporations can get tax deductions for moving jobs overseas, Romney — citing his business experience — says, "I have no idea what you're talking about. ... I may need to get a new accountant."

Update at 9:30 p.m. ET. More Dispute Over Taxes:

The president says again that Romney wants to "cut taxes by $5 trillion and add $2 trillion in spending that the military is not asking for." If the American people think that can be done and they won't end up "picking up the tab ... then Gov. Romney's plan is the one for you," he says.

Romney says, again, that "I'm not in favor of a $5 trillion tax cut. ... That's not my plan." He wants to "bring down rates ... but also bring down deductions at the same time."

Update at 9:19 p.m. ET. Differences On Job Creation, Taxes:

The first question from Lehrer is about jobs. "What are the major differences between the two of you about how you would go about creating jobs?"

Obama first says the most important point he wants to make is that "20 years ago I became the luckiest man on Earth because Michelle Obama agreed to marry me."

He then goes on to say that four years ago the nation was facing the worst economic crisis since the Great Depression. He cites the creation of about 5 million jobs since he took office. But more work needs to be done, he says.

Romney, says Obama, believes that cutting taxes alone will get the economy moving. "I think we've got to invest in education and training" and take other steps, Obama says.

Voters, he says in a reference to GOP positions, need to decide whether they want to "double down on the policies that got us into the mess."

Romney begins by congratulating the Obamas on their wedding anniversary, and jokes that "this was obviously the most romantic place you could imagine ... Here with me."

Then Romney begins drawing differences with the president. "It's going to take a different path" to boost job growth, he says. "My plan has five basic parts": Energy independence. More trade. Training. A balanced budget. And "championing small business."

"The path we've been on is just not successful," says Romney, calling Obama's plan "trickle down government."

Asked by Lehrer to address the president directly, Romney disputes Obama's claim that the GOP candidate has a $5 trillion tax cut plan. "I don't," he says. And he tells Obama that "middle income families are being crushed."

Romney continues on taxes, saying, "I'm not looking to cut massive taxes and reduce the revenues to the government. ... There will be no tax cut that adds to the deficit."

Obama says that "Gov. Romney's proposal ... calls for a $5 trillion tax cut. ... He is saying he's going to pay for it by closing loopholes and deductions. ... He's been asked more than 100 times how he's going to pay for them" and hasn't been able to answer.

"Virtually everything he just said about my tax plan is inaccurate," Romney responds. "I will not reduce the taxes paid by high-income Americans," Romney adds, after joking that as the father of five boys he's used to having someone say something many times even if it's just not true in the hope that it will be believed.

"For 18 months he's been running on this tax plan and now, five weeks before the election he's saying his big, bold idea is 'nevermind,' " Obama says. It's impossible, he says, to enact Romney's plans without either increasing the deficit or raising taxes on the middle class.

Watch for this discussion to be among the several that fact checkers pay close attention to.

Update at 8:55 p.m. ET. Lehrer Tells Audience To "Sit On It!":

Adding to the earlier warning about not making noise during the debate, Lehrer just instructed the crowd that "if you hear something that's really terrific, sit on it! If you hear something you don't like, sit on it!"

He jokingly asked first lady Michelle Obama and Ann Romney, wife of the GOP nominee, to enforce the rules on each of their sides.

Update at 8:45 p.m. ET. No Cheering, Please, Audience Is Told:

With "50 to 100 million" Americans watching tonight, "it's wrong for us to intrude on them," debate commission Co-Chairman Frank Fahrenkopf just told the several thousand people in attendance. "So please, don't clap, don't cheer, don't make any noise."

He also asked those in the building to turn off their cellphones. "Hopefully, we can live for 90 minutes without these things on," Fahrenkopf said.

Fahrenkopf is a former chairman of the Republican National Committee. The other commission co-chairman is Mike McCurry, one-time press secretary to Democratic President Bill Clinton.

Update at 8:35 p.m. ET. What Does Each Man Need To Do?

On All Things Considered today, NPR's Mara Liasson said the conventional wisdom holds that Romney "has the bigger task." He needs, she said, to "criticize the president without looking too harsh or negative." And Romney must "show how his economic policies can make people's lives better in the future."

One advantage Romney has, Mara said, is that he comes in "as an underdog." So the expectations are lower for the Republican.

President Obama, she said, must "avoid a mistake ... [and] not come off as smug or arrogant or thin-skinned."

As for how important the debates may be, Mara said it's "hard to find an example since the Kennedy-Nixon debates" in 1960 when they appeared to significantly affect the outcome of an election. But in a race that's likely to be "decided by a hair," said Mara, "little things really do matter" and a good or bad debate performance could be important.

Update at 8:25 p.m. ET: What's The Format? What Are The Topics? According to the Commission on Presidential Debates, tonight's debate will be divided into "six segments of approximately 15 minutes each. ... The moderator will open each segment with a question, after which each candidate will have two minutes to respond. The moderator will use the balance of the time in the segment for a discussion of the topic."

A coin toss has determined that President Obama will get the first question. Romney will get the last word before the debate ends.

Domestic policy is the overall topic tonight. Lehrer has announced that he plans to focus on the economy in the first three segments. After that, he plans to move to health care, "the role of government," and "governing."

As The Christian Science Monitor notes, in past years "debates have typically had more questions and shorter discussion times. Lehrer, in part, advocated for the new format, and pushed to reduce the number of questions from nine to six, in the hopes that it would encourage more of a television talk-show approach, in which the candidates engage in discussion rather than just deliver talking points."

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