The news of another open Supreme Court seat went off like a bomb on Capitol Hill on Wednesday. “The Republican reaction I’ve seen so far has been universal,” a G.O.P. Senate aide told me shortly after Anthony Kennedy—a center-right justice and frequent swing vote over the past three decades—announced his retirement. “We are very psyched.” Conservatives have reason to celebrate: for many, the ideological slant of the high court was the biggest political trophy at stake in the 2016 election, and one of the reasons many evangelical voters pinched their noses and voted for Donald Trump. The situation for Democrats, meanwhile, is desperate. After stonewalling Obama nominee Merrick Garland in 2016, tut-tutting about the propriety of rebalancing the Supreme Court during an election year, Senate Majority Leader Mitch McConnell vaporized the ability of the minority party to filibuster Trump’s own pick, Neil Gorsuch, deploying the so-called “nuclear option” to run roughshod over the opposition.

Now, with effectively no check on Trump’s ability to control the destiny of the court, the far right could assert its ideological power for a generation. “It is momentous. Justice Kennedy was a center-right Justice, and the president looks like he intends to nominate a far-right one,” said Neal Katyal, a former Obama administration solicitor general who has argued 37 Supreme Court cases before Kennedy. “Even had the abhorrent treatment of Merrick Garland by Senate Republicans not occurred, the potential shift in alignment in the ninth seat means that this would be a very important nomination, impacting everything from reproductive rights to immigration to criminal justice.”

Democrats are particularly worried about social issues like abortion and same-sex marriage that they consider settled. While Kennedy usually leaned to the right in his 30 years on the Supreme Court, the Reagan nominee also sided with the court’s liberals in all four of the landmark gay-rights cases during his tenure. With a solid five-four conservative majority, legal experts warn, many of those progressive achievements could be undone. “It would take little movement to the right in a new nominee to produce sweeping changes in cases across a dozen areas,” Jonathan Turley, a constitutional law professor at George Washington University, told me. “While Kennedy’s legacy is immense, it is also the most vulnerable of any justice on the court. Most of his legacy hangs by a single vote—his own.”

Assuming that Trump’s nominee is to the right of Kennedy, the fate of landmark cases like Roe v. Wade and Lawrence v. Texas—in which Kennedy cast the critical swing vote—could rest with Chief Justice John Roberts, the court’s next most conservative judge after Kennedy. “His life is about the get very difficult,” Turley said. “Roberts is not someone who likes to see sweeping social changes mandated by the court. But while I think Roberts would resist a frontal attack on Roe v. Wade, he may accept some significant inroads along the edges. And that is what I would expect happen.” After all, Roberts has previously declined to join opinions calling on Roe to be reversed, but history suggests the chief justice could assent to decisions that would place significant restricts on abortion and abortion access. “They can effectively kill Roe v. Wade by a thousand paper cuts.”

Unless Democrats retake the Senate in November—and somehow manage to prevent Republicans from confirming a Trump nominee in the months before—there is virtually nothing they can do to prevent the president from putting his pick on the bench. (Appeals court judges Thomas Hardiman and Brett Kavanaugh appear to lead Trump’s short list, which includes some two-dozen names.) Minority Leader Chuck Schumer tried to argue on the Senate floor Wednesday that McConnell should follow his own rule and not consider a Supreme Court nominee in an election year, but was immediately shot down. As former Republican majority leader Trent Lott told me, summing up the G.O.P. view, “this is not a presidential election year.”