Sen. Kirsten Gillibrand of New York is endorsing a Democratic challenger to Rep. Daniel Lipinski (D-Ill.), making her the first presidential contender to wade into a down-ballot Democratic primary.

At a Democratic Party event in Chicago, Gillibrand endorsed Marie Newman, a liberal activist who narrowly lost to Lipinski in 2018.

“She’s got a tough race in front of her, but I promise you, Marie will represent her district better, and she will represent all of us better,” Gillibrand said. Moments earlier, Newman had endorsed Gillibrand’s presidential campaign.

Lipinski, one of just three House Democrats who regularly co-sponsors antiabortion legislation, has faced primary challenges in three of his eight elections.

He won his first term, in 2004, when his father retired from the House and local Democrats put the younger Lipinski on the ballot, a decision that rankled some Chicago-area activists.

Newman, who had never run for office before 2018, gave Lipinski the toughest challenge of his career. She secured endorsements from two of the congressman’s Illinois colleagues, Reps. Jan Schakowsky (D) and Luis Gutierrez (D), and was backed by a coalition of abortion rights and gay rights groups, which had clashed with Lipinski.

The challenger was also endorsed by Gillibrand, who held a fundraiser for her in early 2018, and by Sen. Bernie Sanders (D-Ill.), who endorsed her after a campaign trip to Chicago. Sanders’s campaign could not comment on whether he would weigh in on the race this year.

After the 2018 midterms, when two of Lipinski’s colleagues lost primaries to challengers from the left, the Democratic Congressional Campaign Committee issued a new rule that would prevent contractors who worked against incumbents from doing business with the party’s official campaign arm.

Illinois’s 3rd Congressional District, which stretches from Chicago to some of the city’s southwest suburbs, has been represented by a Democrat since 1975. In 2016, Hillary Clinton carried the district by 15 points, but Sanders had carried it by eight points during that year’s presidential primary, a fact that made activists optimistic about unseating Lipinski.

In 2018, after pushing past Newman, Lipinski carried the district by 48 points; Republicans had denounced their nominee, a white supremacist who had secured the party’s nod after no other candidate stepped forward.