President Donald Trump is finally in the crosshairs of the #MeToo movement. Four women who have accused him of sexual misconduct repeated their allegations on Monday—that Trump ogled, groped, and kissed women without their consent. In response, New York Senator Kirsten Gillibrand joined a growing list of prominent Democrats who have called for Trump’s resignation. “President Trump has committed assault, according to these women,” she said on CNN. “And those are very credible allegations of misconduct and criminal activity, and he should be fully investigated and he should resign.”

Trump has “complained privately that the avalanche of charges taking down prominent men is spinning out of control,” according to Politico report on Monday, so it was hardly a surprise when, on Tuesday morning, he attacked the female politician who has been most vocal about holding powerful men to account:

Though limited to 280 characters, Trump managed to hit many sexist tropes: women are weak (“lightweight), women are subservient (“flunky” and “begging”), women are duplicitous prostitutes (“would do anything for them”), women are betrayers (“very disloyal”). Gillibrand’s response was righteous and steadfast:

Once sexual harassment became a pressing political topic, it was inevitable that these two would clash. It’s not just that Trump has been accused of misconduct more than a dozen times, and has a well-documented history of demeaning and belittling women; he also rose to the presidency by fomenting sexist doubts about his opponent Hillary Clinton. Gillibrand, meanwhile, has made combating sexual harassment and assault her signature issue, more so than any other politician in America. She hasn’t shirked from policing her own side, either. She was the first Democratic senator to call on her colleague Al Franken to resign, and she’s broken with party orthodoxy on Bill Clinton, saying that he should have resigned once the facts of the Monica Lewinsky scandal were known.

The contours of the Trump/Gillibrand feud lay out the political landscape of contemporary America, and could prefigure the role gender politics will play in the 2018 and 2020 elections. Still, for Gillibrand and the Democratic Party, there remains the problem of how to combine critiques of particular men like Trump, which are popular with the party’s base, with a broader policy agenda for fighting sexual harassment—one that appeals to nonpartisans, too.

The GOP response to Trump’s tweets shows how challenging that will be. While the president and Gillibrand traded blows, some Republicans in Congress didn’t just refuse to comment; they refused even to be told about the contents of the tweet:

Iowa Senator Joni Ernst took a similar tack:

The unwillingness of major Republicans even to acknowledge the contents of Trump’s tweets suggests how radioactive they are. College-educated white women, traditionally a mainstay of the GOP, are drifting away from the party in the Trump era. The president’s antics will make the problem worse, which presents an opportunity for Democrats like Gillibrand. As she emerges as a national leader and a strong contender for the Democratic presidential nomination in 2020, her main task will be to convert the bold stance she’s taken against men like Franken and Trump into an expansive message about achieving gender equality in America.

Since 2012, when she saw the documentary The Invisible War, Gillibrand has been on the forefront of pushing for the military to crack-down on sexual abuse. Her tough grilling of military leaders has earned her enemies in her own party, including stalwart Pentagon allies like Senator Claire McCaskill and now-retired Senator Carl Levin. Gillibrand’s signature reform measure, the Military Justice Improvement Act, has met with resistance because it would weaken the power of military commanders in overseeing rape and assault cases. It fell five votes short of the 60 needed, but gained genuine bipartisan traction.

The test for Gillibrand will be on the policy front. Can she turn the anger of the #MeToo moment into a lasting political movement by mainstreaming an agenda that puts gender equality front and center? Such an agenda would carve out a political niche for Gillibrand, but it’s also risky, as it could be seen as narrower than, say, the economic populism of senators Bernie Sanders and Elizabeth Warren. As the example of the Military Justice Improvement Act shows, Gillibrand will face resistance in her own party. Moreover, Trump and other Republicans will try to stoke an anti-feminist backlash.

That’s not likely to stop Gillibrand. She has shown, in her campaign to reform the military, that she has the political courage to stake out a controversial position. And to her credit, she has always seen sexual misconduct as a systematic problem, going beyond the misdeeds of a few men. So while she might be calling on Trump to resign, this is surely just the beginning of a serious effort at broader institutional reforms.

There’s an element of political theater to calls for Trump’s resignation, since they obviously won’t lead to his removal. But the real goal is to use Trump’s undeniable sexism to make issues of sexual harassment visible and politically salient. If Gillibrand is sworn in as president in 2021, it’ll be because Trump was the ideal foil for her. He might yet have a lasting legacy in helping elect the first woman president.