The first few minutes of the Democratic debate on CNN between Hillary Clinton and Bernie Sanders were quite cordial. But that didn't last long.

Taking place in Flint, Mich., the town that has been thrust into the national spotlight amid its water crisis, the two candidates took questions from the audience about their plans to help the heavily African-American city recover and restore clean water to all its residents.

But as the debate wore on, the two rivals had one of their testiest exchanges yet as discussion moved to trade policies, the auto bailout, Michigan's struggling economy and gun control.

Michigan is an important political test for both Democratic candidates. Its 147 pledged delegates will be up for grabs on Tuesday, where polls show it's the former secretary of state who has an edge over the Vermont senator.

Here are some of the top moments.

Focus on Flint water crisis

Both candidates used their opening statements to address the devastating water crisis in Flint. Sanders reiterated his earlier call for Republican Gov. Rick Snyder to resign over the scandal, saying "his dereliction of duty was irresponsible."

"Amen," Clinton echoed, calling for the first time as well for Snyder to step down or to face a recall election.

"We must focus on what should be done for people of Flint," Clinton said, reminding the audience it was her idea to hold a debate in Flint. "It is raining lead in Flint, and the state is derelict in not coming forward with the money that is required."

Sanders told one woman from the audience, who were questioning the candidates, that it was a disgrace that his water bill in Vermont was lower than ones in Flint right now.

"The first thing you do is say people are not paying a water bill for poisoned water," Sanders thundered.

Both were pressed on whether they had waited too late to visit the embattled community and whether they were only pushing the issue for political gain and would abandon the fight after the election.

"When I heard about it, I immediately sent people here to find out what was going on. It was almost unbelievable," Clinton said. She pledged that as president she would rid the country of lead pipes everywhere within five years to prevent another Flint-like crisis and would stay with the city "in whatever capacity I am."

Sanders dings Clinton on trade: She's "found religion"

Questions from Flint residents moved on to how to protect jobs in the state, especially the state's troubled auto industry. Clinton explained how she would incentivize manufacturing.

But Sanders pounced, calling her out on having an inauthentic change of heart on one of his most passionate issues.

"I am very glad that Secretary Clinton discovered religion on this issue, but it's a little bit too late," he argued. "Secretary Clinton supported virtually every one of the disastrous trade agreements written by corporate America."

He slammed her for past support of trade agreements like the North American Free Trade Agreement, which was implemented under President Bill Clinton, and for being late in opposing the more recent Trans-Pacific Partnership.

But Clinton turned the tables, arguing that Sanders opposed the auto bailout that helped to salvage many jobs in the state.

"The money was there, and had to be released in order to save the American auto industry and 4 million jobs, and to begin the restructuring. We had the best year that the auto industry has had in a long time. I voted to save the auto industry," Clinton said.

Sanders underscored his passion for the issue, though, embracing a frequent criticism that he's too focused on inequality during his campaign.

"I'm a one-issue person, well, I guess so," he said. "My one issue is trying to rebuild a disappearing middle class. That's my one issue."

The two also disagreed on whether the Export-Import Bank should be renewed — something conservatives oppose and that Sanders has been a lone voice of Democratic opposition on. He argued that the bank benefits big corporations, such as Boeing and Caterpillar, while Clinton argued it's necessary to protect American jobs and keep them in the U.S.

Things get testy: "Excuse me, I'm talking"

The trade issue prompted one of the most tense exchanges between the two candidates. As Sanders tried to rebut Clinton's claims, he interjected, "Excuse me, I'm talking."

"When billionaires on Wall Street destroyed this economy, they went to Congress and they said, 'Please, we'll be good boys, bail us out,' " Sanders continued. "You know what I said? I said, 'Let the billionaires themselves bail out Wall Street.' It shouldn't be the middle class of this country."

Clinton tried to interject, but he again cut her off, telling her, "Wait a minute. Wait. Could I finish? You'll have your turn, all right?"

Later, when the conversation turned to gun control, he again jumped in: "Can I — can I finish, please? All right?"

The succession of exchanges recalled Clinton's first campaign for office in 2000, when Republican Rep. Rick Lazio was criticized for going after Clinton during their New York Senate debate in a way some saw as sexist.

That's a comparison the pro-Clinton group Correct the Record was happy to make, blasting out the clip and calling it Sanders' "Rick Lazio moment."

Historically, male politicians have had to walk a fine line in coming across as too aggressive against female politicians — and if Clinton is the nominee, it's an issue Republicans will have to find a way to handle as well. While this hasn't been a big problem for Sanders before, it was clear Clinton was getting under his skin on issues he's very passionate about. And it's a moment you can expect to see again, more than likely.

Wall Street speeches dog Clinton

One thing Clinton still hasn't found a good answer to is why she won't release transcripts of speeches she was paid to give to Wall Street groups. And as talk turned to bailouts, Sanders saw another opening to hammer her on it.

"Now, I kind of think if you get paid a couple hundred-thousand dollars for a speech, it must be a great speech. I think we should release it and let the American people see what that transcript was," he said.

"And I have said and I will say again, I will be happy to release anything I have as long as everybody else does too, because what really is behind that question, Republicans and Democrats, is where I can stand up to Wall Street," she argued, putting the onus on potential GOP rivals to release full records as well.

But for Sanders, the comeback was easy.

"All right, look, Secretary Clinton wants everybody else to release it, well, I'm your Democratic opponent, I release it, here it is," he said, throwing his hands up in exasperation. "There ain't nothing. I don't give speeches to Wall Street for hundreds of thousands of dollars. You got it."

Gun control trips up Sanders

If Clinton's Wall Street ties are her Achilles' heel, then Sanders' past opposition to some gun control measures is his.

The father of a girl who was shot in Kalamazoo, Mich., by an Uber driver last month pressed the candidates on stricter gun control measures, noting the alleged shooter had no criminal or mental health background that would have prevented him from getting a gun.

"We've got to have a public discussion, because we have created a culture in which people grab for guns all the time," Clinton said, criticizing Sanders for a past vote for immunity from lawsuits for gun sellers.

Sanders argued there was no "magic solution to this problem."

"Any lunatic tomorrow, any person can walk into a theater and do something horrific. And you know what? For us to tell you that that absolutely will not happen would be untrue," he said.

Pressed on the immunity vote by moderator Anderson Cooper, Sanders was forced into a full-throated defense of it — not something that usually plays well in a Democratic primary.

"If you go to a gun store and you legally purchase a gun, and then, three days later, if you go out and start killing people, is the point of this lawsuit to hold the gun shop owner or the manufacturer of that gun liable?" Sanders argued. "If that is the point, I have to tell you, I disagree. I disagree because you hold people — in terms of this liability thing, where you hold manufacturers' liability, is if they understand that they're selling guns into an area that it's getting into the hands of criminals, of course they should be held liable."

Clinton went for the emotional heartstrings in her response, though.

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