In the spring of 2011, the notion of any Democrat taking back Scott Brown’s Senate seat seemed unlikely. Statewide his approval rating was at 73 percent, according to private polling by the Democratic Senatorial Committee, and in potential and actual matchups with Democrats he led by double digits.

Brown is a genuine celebrity and he campaigns hard. On the campaign trail he is mobbed by well-wishers, and almost all of them want to take a photo with the former model and magazine centerfold.

Independent voter Louis Cook — the kind of voter that Brown needs to win — greeted the senator at a restaurant in Watertown recently and said, "He’s the best thing that could happen to us and I hope he runs for President some day."

So to beat Brown, Democrats concluded in 2011 that they needed a star of their own. Consumer advocate Elizabeth Warren announced her candidacy in Framingham and online saying, "I’m going to do this. I’m going to run for the United States Senate."

But as Warren’s campaign rolled out pundits suggested that the race was still Brown’s to lose by virtue of the polls. She was nine points behind in September 2011. Brown seemed unbeatable. How did he get to that vaunted point in his political career? In the winter of 2010, Brown, then a state Senator, rode a tsunami of Tea Party anger to an upset victory over Attorney General Martha Coakley.

"We basically got him elected to oppose Obamacare, the health care reform bill," said Christine Morabito, president of the Greater Boston Tea Party. We spoke over breakfast at Denny's in Lawrence. She is a fan of Brown's, but she is also disappointed in his voting record: "He was never as ideologically conservative as the Tea Party."

But Brown's reputation for independence is popular with crossover voters like Helen Truscott of Brookline, who said, "I think he’s going to do a lot for us and I like the way he’s very bipartisan. He goes on both sides."

Brown also votes on both sides: He voted against three Obama jobs bills and joined Democrats in voting to end the “Don’t Ask, Don’t Tell” policy on gays in the military. He has voted for the Blunt Amendment that would allow employers to deny coverage for contraception on the grounds of religion while also opposing an effort to cut off federal funding for Planned Parenthood. Brown has also pledged to scuttle the president’s signature health care law — a position that helped fuel Warren’s rise in the polls. In April, as her numbers rose, the Boston Herald published a story questioning whether Warren had used her avowed Native American heritage to gain advantage in the academic job market. Brown seized on the issue, which he saw as a potent weapon against his Democratic opponent.

In the first and second debates, Brown candidly laid out his position: "She checked the box claiming that she’s a Native American and clearly she’s not." Throughout the spring, summer and fall, Brown hammered Warren and succeeded in raising questions about her character — but at the expense of his own likability. And in September the issue backfired completely when Brown supporters rallied outside South Station shouting mock Native American war cries.

"What I didn’t understand was the disrespect," said Joanne Dunne of the North American Indian Center of Boston. Dunne had had earlier criticized Warren’s handling of the Native American controversy. But she was downright irate over the actions of Brown’s staff members even though Brown himself apologized.

"This might have resonated a little bit had Scott Brown fired every single person that was out there protesting and making war cries," Dunne said.

In September Brown pivoted to a new line of attack. At a press conference, he described his opponent as a "hired gun" for large corporations. In October, Brown began running an ad using a female narrator who says, in part, "The Globe says Elizabeth Warren was a key lawyer in an asbestos case working for a big corporation. Warren helped Travelers Insurance restrict payments to victims of asbestos poisoning. The results were disastrous for the victims. The insurance company saved millions. And Elizabeth Warren got paid 40 times what they paid victims. Elizabeth Warren’s just not who she says she is.”

But The Boston Globe found that charge “misleading,” as Brown failed to point out that Warren expected Travelers to pay out a settlement of $500 million to asbestos workers. Brown’s straight-shooter reputation was further eroded by a false claim that Warren used actors in her ad rebuking the asbestos allegation.

Political experts believe that Brown has about a 50/50 chance of keeping his seat and he is running like someone who knows it. The senator is a long way from the spring of last year when some Democrats believed him to be unbeatable. Brown is still popular in the state and few would be surprised if he pulls off a win. But he is leaving little to chance. Over the summer in Tampa — the site of the Republican National Convention — Brown met with GOP political strategist Karl Rove in what he described as a chance encounter. Brown is looking for political advantage wherever he can find it in the hope again of shocking the nation as he did in 2010.