SPRINGFIELD, Mass. – Democratic U.S. Senate candidate Elizabeth Warren won her party’s overwhelming endorsement Saturday, shutting out a potential primary election opponent and becoming the presumptive nominee to face Republican Sen. Scott Brown in what is expected to one of the nation’s most expensive and closely watched Senate races.

Warren won the votes of 95.7 percent of the more than 3,500 delegates to the state Democratic convention, the largest margin of any candidate in a contested race in the party’s history.

Marisa DeFranco, an immigration attorney from Middleton, had waged a longshot campaign for Senate but finished far below the 15 percent she needed under party rules to get on the September primary ballot. Democratic party chairman John Walsh had said as early as Saturday morning that he expected DeFranco to reach the threshold.

For Warren, the gathering of party loyalists presented an opportunity to regain momentum for her campaign after struggling for weeks to put behind her a controversy over her claims of Native American ancestry.

Addressing the delegates before the vote, Warren said Brown would rather attack her family than talk about his own voting record.

“Well, I say this: If that’s all you’ve got, Scott Brown, I’m ready,” said Warren to sustained applause.

“And let me be clear: I am not backing down. I didn’t get in this race to fold up the first time I got punched,” she said.

Warren, who called Brown a “Mitt Romney Republican” and a “Wall Street Republican,” listed a series of votes the incumbent had made, including votes against a Democratic bill to prevent a doubling of student loan interest rates and in favor of big oil subsidies.

She also invoked the memory of the late Democratic Sen. Edward Kennedy, who for 47 years held the seat that Brown won in a special election in 2010.

“It’s a long way from Ted Kennedy to Scott Brown,” said Warren.

In the days leading up to the convention, Warren made perhaps her most concerted effort to address several weeks of questions about her past references to Native American ancestry, which she has not documented.

First, Warren acknowledged that she had told Harvard Law School and her previous employer, the University of Pennsylvania, of her Native American heritage, but said she did so after she was hired and that it had never been a factor in advancing her academic career.

In a series of interviews Friday, Warren also provided more detail about the “family lore” that had convinced her of Native American ancestry. She said her mother and father had been forced to elope because of her mother’s heritage.

Warren attributed the her lag in addressing the controversy to needing more time to go back and recall details of events that had occurred decades ago.

DeFranco has little name recognition and through the first quarter of the year had raised just over $41,000 for her campaign, compared to the $15.8 million that Warren’s campaign had pulled in.

“For those of you who know me I don’t scare easily. I have a proven track record of … taking on long odds and winning,” said DeFranco in asking for the votes of the delegates.

“Let’s have a good and healthy primary and go after Scott Brown” together, she said. “We’ll be stronger for it.”