Stacey Abrams made history on Tuesday night by winning the Democratic gubernatorial primary in Georgia, becoming the first black woman nominated for governor by a major party. If she defeats her Republican opponent in the fall, she’ll make more history yet. “There have been nearly 9,000 opportunities for a black woman to have been the governor of a state in a year,” Philip Bump noted in The Washington Post, “but of those, all but 331 have gone to white men. More than 850 of those opportunities—81.1 percent—have gone to white men.” Nearly all of the remaining opportunities went to white women and men of color, with two exceptions. A black woman has never become governor.

Yet there are signs that 2018 is a major turning point, at least for one party. Abrams’s win wasn’t an outlier but part of a major trend: The Democratic Party is nominating more women than ever, while the Republican Party moves in the opposite direction. “With wins for female House candidates in Kentucky (Amy McGrath in KY-6), Texas (Lizzie Fletcher in TX-7 and Gina Ortiz Jones in TX-23) and also in Georgia, the total number of female House nominees is already up to 72—with 62 of those being on the Democratic side,” Benjy Sarlin of NBC News observed on Wednesday. “As of last night’s primaries, more than 40 percent of Democratic nominees so far are women, compared to less than 10 percent for Republicans.”

A chart provided by Boston College political scientist Dave Hopkins confirms that a historic shift is underway, with the two parties taking divergent paths on gender:

As recently as the 1980s, the two major political parties were roughly equal on gender—which is to say equally unequal, with men making up roughly 90 percent of incumbents in the House of Representatives. A gap between the parties opened up in 1992, with a steep increase in the number of women running as Democrats, but that doesn’t compare to what has happened in 2018. Democrats are fielding about four times as many female candidates as the GOP.

The much bigger story, though, is the gender gap between the two parties overall, which is the result of divergent policies on social issues. This persistent, widening gap illustrates the social science concept of “path dependence”: that the decisions you make in the past foreclose the range of future choices. If a city continues to build more highways, rather than subway lines, it becomes all the more difficult to reverse course and shift from a car culture to a public transit one.

Consider how the two major parties have handled race. In the 1960s, the Democrats embraced civil rights while the Republicans adopted the “Southern strategy” of exploiting the white backlash. This initial decision made both parties indebted to constituencies which pushed them farther down the path they had chosen, so the Democrats became ever more committed to racial liberalism while the Republicans engaged in dog-whistle racism that paved the way for Donald Trump’s revanchist white nationalism.

What’s true of race also applies to gender. As recently as the 1960s, the two parties were not markedly different on gender issues. The Republicans had their share of sexual liberals and feminists (including Planned Parenthood founder Margaret Sanger, in the last years of her life) while the Democrats had many social conservatives (including George Wallace). After the upheaval of the 1960s, activists on both sides of divisive issues decided to take over different parties. Feminist and LGBT activists found a home among Democrats, albeit with some resistance, while the religious right conquered the Republicans.

This sorting has set the parties on seemingly irreversible paths, with the Democrats increasingly committed to feminism and the Republicans more forcefully defending traditional gender norms. What is Donald Trump, with his boasts of grabbing women by the genitals and his assurances of his penis size, if not the embodiment of the idea that men have an innate right to rule?

That Trump is the GOP’s standard-bearer seems to be pushing women away from the party, both as candidates for office and voters. As Politico notes, “According to a Pew Research Center survey in March, 56 percent of American women identify as Democrats or lean Democratic, a 4 percentage point increase over 2015. The Democratic Party’s advantage among younger voters is even greater with women, with 70 percent of millennial women identifying themselves as Democrats or leaning Democratic.”

In policy terms, this path dependency is likely to push both parties further from the center, deepening political polarization. The GOP likely will continue to stoke culture wars on abortion and LGBT issues, as Trump is doing now by banning transgender people from the military and pushing a rule to prohibit doctors from advising patients on where to receive abortions. This will further drive women from the party, leading to even fewer female candidates.

Conversely, Democrats will move further left on gender issues as women comprise a bigger percentage of their base. “The prospect of a record number of female candidates on the November ballot—and running for president in 2020—has Democratic leaders leaning into increasingly explicit, gender-based appeals and focusing renewed attention on education, health care, sexual harassment and other issues perceived as critical to women,” Politico reported.

Stacey Abrams is evidence of this trend. She’s not trying to hug the center, but running as an outspoken progressive. “While extolling her success in working with Republicans while minority leader, Ms. Abrams emphasized her progressive positions on issues like expanding Medicaid in the state, along with the personal challenges she had overcome as an African-American from a family of modest means,” The New York Times reported. “Rather than focusing on increasing the Democratic share of the vote among moderate-to-conservative whites, Ms. Abrams emphasized her ability to energize and mobilize young voters and the state’s growing nonwhite electorate.”

Georgia is a tough place for Democrats. Abrams might not win in November, but she’s clearly a harbinger of Democrats future: more women, more people of color, and more unabashed progressives.