Specifically, Public Citizen accused him of misrepresenting the results of past trade agreements.

Ms. Wallach’s role as antagonist to Mr. Froman has been decades in the making. At Harvard, the two ran in very different circles. The closest they came was a small campus building that housed both The Harvard Law Review, where the future president and his future trade negotiator were editors, and the Harvard Legal Aid Bureau, where she was an officer.

As for the future president, Ms. Wallach worked with him during a divisive campaign to bring more diversity to the Harvard Law faculty and again on an effort to save Harvard’s program advising law students on public interest careers, said John Bonifaz, a campaign finance reformer and Wallach ally who was at Harvard at the time.

Mr. Froman was part of neither effort.

“He was more a corporate law type,” Mr. Bonifaz said. “A lot of people at law school were focused on going out and making a ton of money.”

In fact, that was not Mr. Froman’s initial career path. Straight out of law school, he went to Albania to help that tiny impoverished nation’s legal system. He spent most of the 1990s in the Clinton administration, at the White House and at Treasury, finally following Treasury Secretary Robert E. Rubin to Citigroup in 2001, only to return to Washington in 2009 to join the Obama White House as an emissary to international economic organizations.

Through it all, his path kept crossing Ms. Wallach’s. In 1998, she bedeviled the Clinton administration with her campaign to deny the president new fast-track trade authority, a fight her side won. In 1999, as Mr. Rubin’s chief of staff at Treasury, Mr. Froman clashed with her over international efforts to expand the World Trade Organization, a campaign that died after anti-globalization activists rioted in Seattle.

Recalling her appearance before Citigroup executives at Mr. Froman’s behest, she said that ultimately she did not take the $20,000 speaking fee, settling for her standard, much smaller amount and a commercial flight. She told the executives that trade agreements were protecting corporations at the expense of poor people, keeping pharmaceutical prices high and access to food difficult.