With Joe Biden’s entry into the Democratic presidential race last week, there are now at least 20 candidates vying to challenge President Donald Trump next November. They run a wide gamut of ideological stances, from the democratic socialism of Bernie Sanders to the reformist liberalism of Elizabeth Warren to the nostalgic centrism of Biden, Beto O’Rourke, and Cory Booker. Those differences are important. But they’re ultimately not as important as their Supreme Court nominees.

Trump partially owes his presidency to a quirk of fate: Justice Antonin Scalia’s sudden death in February 2016. When Trump became the presumptive nominee in the ensuing months, most conservatives rallied around him out of desperation to prevent Hillary Clinton from filling the vacancy. With Democrats now entering a bruising primary season, it’s an open question whether the party will similarly unite to prevent Trump from replacing a justice like Ruth Bader Ginsburg—no matter the eventual nominee.

Scalia’s death was a psychic shock to the Republican Party, which held the longtime justice in as much esteem as liberals hold Ginsburg, and it left the court evenly split between four conservative and four liberal justices. Senate Republicans, led by Mitch McConnell, quickly declared that they would not consider whomever Barack Obama named to replace him—and followed through by ignoring nominee Merrick Garland. That strategy effectively bound the court’s fate to the outcome of November’s election. Conservatives rose to the challenge, rallying around the Republican candidate despite his flaws.

“I believe if Justice Scalia had not passed away when he did that there’s a very good possibility Hillary Clinton would be president of the United States right now,” Texas Senator Ted Cruz remarked last June after Anthony Kennedy’s retirement. Cruz’s own endorsement of Trump in 2016 proves his point. He famously spurned Trump during a primetime speech at the Republican National Convention that year, telling a national audience to “vote your conscience.” When he eventually did endorse Trump the following September, Cruz cited Trump’s list of prospective Supreme Court nominees as the foremost deciding factor.

“For anyone concerned about the Bill of Rights—free speech, religious liberty, the Second Amendment—the Court hangs in the balance,” he wrote in a statement announcing the decision on Facebook. “I have spent my professional career fighting before the Court to defend the Constitution. We are only one justice away from losing our most basic rights, and the next president will appoint as many as four new justices. We know, without a doubt, that every Clinton appointee would be a left-wing ideologue. Trump, in contrast, has promised to appoint justices ‘in the mold of Scalia.’”