WASHINGTON — Former Sen. Scott Brown won a surprising ally in his quest to become President-elect Donald Trump's Veterans Affairs secretary: Massachusetts Sen. Elizabeth Warren.

Warren, a leader of the Democratic left and one of Trump's sharpest-tongued critics, has been a longtime nemesis of Brown.

She defeated him in 2012 in one of the most bitter and costly Senate elections in recent years, then campaigned against him two years later when he tried in vain to win a Senate seat in neighboring New Hampshire and has mocked him ever since as “the biggest loser.”

Brown, a Republican, has been one of Warren's harshest critics too, making her undocumented claims of Native American heritage a central campaign issue in their 2012 race. Trump latched onto it when he referred to Warren repeatedly as “Pocahontas” throughout his own public feud with her.

As recently as June, Brown challenged Warren to take a DNA test to prove her ancestry and attacked her for “character flaws” while speaking on Trump's behalf.

Such bitter animosity has faded, Brown said.

Relations between the two have been thawing for a while, he said, at mutual appearances including a recent celebration in Boston for an employee who worked in both of their Senate offices handling constituent problems.

Brown said that Warren, her husband and her staff made him and his family feel especially welcome as they celebrated the employee, who had been a holdover from the time when their Senate seat was occupied by Edward Kennedy.

On Thursday night, Warren phoned Brown and they spoke for 15 minutes about their families, veterans and Senate dysfunction, Brown said. Warren's office confirmed the call.

Brown said he remembers the barbs between him and Warren, and he did not quite apologize for his end.

But he spoke humbly about the need to move on.

“We've been trying to tone things down for quite a while,” Brown said in an interview. “She won. I lost. She was jabbing at me, and I was jabbing at her. …

“It wasn't who I am. I (am) a better person. I don't mind disagreeing on politics and policy. The personal stuff, as I get older, I'm trying to be better.”

Warren made her support for Brown public Thursday on WGBH radio in Boston while criticizing Trump's pick for Treasury secretary, Steven Mnuchin, whom she derided as “a man who was responsible for turning the lives of millions of people upside down financially.”

Warren had kinder words for Brown.

“If Scott Brown is the nominee for Veterans Affairs, I have no doubt that he would put his heart and soul into trying to help veterans, and I would put my heart and soul into trying to help him do that,” she said. “You bet I'd support him for that.”

Warren also gave support, albeit more qualified, for former Massachusetts Gov. Mitt Romney as a potential secretary of state.

Brown thanked Warren on Twitter, and added in his interview that he was gratified that some of Warren's liberal supporters sent him social media messages pointing to Warren's validation as the basis for their newfound trust.

Brown, who retired from the National Guard in 2014 after 35 years, has been a longtime veterans advocate dating to his days as a state senator. He has no significant administrative experience, which could hinder his bid in running a sprawling bureaucracy that will be central to fulfilling Trump's campaign promise to repair the agency and improve veteran care.

But he was an early and enthusiastic Trump endorser in New Hampshire, where he now lives, and seems to have a strong relationship with Trump.

Former Alaska Gov. Sarah Palin has also been reported as a potential candidate for the job, which may help Brown in winning support from senators who find her too polarizing.

Warren's three brothers served in the military, and Brown said the commitment to veterans that he and Warren share is sincere.

The detente has drawn some skepticism.

“Maybe she's damning him with excessive praise,” said Rob Gray, a veteran GOP political operative in Massachusetts.

Brown dismissed that theory. “We are people first,” he said. “This isn't about me or her or Trump or anybody making criticisms. It's about our veterans.”

noah.bierman@latimes.com