Photo: AP

Hillary Clinton and Elizabeth Warren have a complicated history. But on Monday, the senior senator from Massachusetts will appear with the former secretary of state on stage at a campaign event for the first time.

Warren will speak for the presumptive Democratic nominee at a rally in Cincinnati, according to the Associated Press, amid ongoing reports that she is being vetted as a possible vice-presidential candidate. Lately, Warren has acted as one of Clinton’s strongest anti-Donald Trump surrogates. (Trump has not taken her criticism well.)

In fact, Warren has turned her dry skepticism on Clinton herself before. In her 2004 book The Two-Income Trap, Warren recalls a meeting with the first lady in 1998 to discuss pending legislation that would have overhauled bankruptcy laws. Warren convinced Clinton that the legislation should be opposed, and Bill Clinton vetoed the bill at his wife’s behest.

A few years later, as a first-year senator, Clinton voted in support of what was essentially the same bill, after receiving $140,000 in campaign contributions from finance executives. “Big banks were now part of Senator Clinton’s constituency. She wanted their support, and they wanted hers—including a vote in favor of ‘that awful bill,’” Warren wrote.

“The bill was essentially the same, but Hillary Rodham Clinton was not,” she wrote. “Hillary Clinton could not afford such a principled position. Campaigns cost money, and that money wasn’t coming from families in financial trouble.”

Warren detailed their exchange further in an interview with Bill Moyers.

Earlier this month, Warren stopped by Clinton’s campaign headquarters in Brooklyn, telling staffers, “Don’t screw this up!”