President Ronald Reagan nominated the Supreme Court justice who upheld Roe v. Wade. President Trump could nominate the justice who overturns it.

That’s how unpredictable the politics of the Supreme Court can be. Reagan, the most conservative president since the New Deal, arguably did more than any other single political figure to make the Republican Party pro-life. President Trump, widely assumed to be a liberal Trojan horse during the 2016 GOP primaries, was until recently pro-choice.

[Also read: 6 rulings that could be overturned by a post-Kennedy Supreme Court]

Justice Anthony Kennedy also illustrates that unpredictability. He was the Reagan pick who wrote the majority opinion affirming Roe’s core holding. His retirement Wednesday opened the door for Trump to assemble the most conservative Supreme Court in history.

What is predictable is that both parties will keep escalating their war over the composition of the Supreme Court, guaranteeing the confirmation hearings for whomever Trump nominates will be contentious.

[Related: Activists see Anthony Kennedy retirement as chance to upend abortion law]

Democrats are already saying that because Republicans — led by Senate Majority Leader Mitch McConnell, R-Ky. — blocked President Barack Obama’s nomination of Merrick Garland during an election year, then hearings on Kennedy’s successor will have to wait until after the midterm elections this fall.

To do otherwise, says Senate Minority Leader Chuck Schumer, D-N.Y., would be the “ absolute height of hypocrisy .”

“The breakdown in civility and our politics occurred when a sitting President couldn't even get a hearing on a Supreme Court nominee for 8 months,” protested former Obama adviser Ben Rhodes. “Not when someone couldn't eat at Red Hen.”

When it comes to procedural arguments about judicial nominees, there is plenty of hypocrisy to go around on all sides. But it was the Democrats who first realized the high stakes of the Supreme Court confirmation battles. The Garland episode didn’t come out of nowhere.

Kennedy himself is a product of the Democrats’ desire to mitigate the high court’s drift to the Right. He was only nominated after the Senate rejected Robert Bork and Reagan withdrew Douglas Ginsburg.

For conservatives, the third time wasn’t a charm.

Yet on a list of Republican-appointed justices who disappointed conservatives, Kennedy would not rank particularly high. Earl Warren, William Brennan, Harry Blackmun, John Paul Stevens, and David Souter were among the most liberal Supreme Court justices of the past 65 years, all chosen by presidents from the party of Lincoln.

Sandra Day O’Connor was also a mixed bag rather than a consistent originalist, and though no liberal was less conservative overall than Kennedy.

To find an accidental conservative put on the Supreme Court by a Democratic president, you would have to go all the way back to Byron “Whizzer” White under President John F. Kennedy.

Even after Democrats smeared, then rebuffed Bork and then nearly succeeded in doing the same to Clarence Thomas, Republicans voted overwhelmingly to confirm President Bill Clinton’s Supreme Court nominees. Only three GOP senators opposed Ruth Bader Ginsburg, the most liberal Clinton justice.

Half the Democrats in the Senate voted against the impeccably qualified President George W. Bush nominee John Roberts for chief justice. This included Obama, Schumer, Hillary Clinton, and Joe Biden. Only a handful of Democratic senators supported the confirmation of Samuel Alito.

The days of Antonin Scalia being confirmed unanimously are over. And even that was partly the result of Democrats preferring to block William Rehnquist's promotion to chief justice.

It was not until Obama’s nominations of Sonia Sotomayor and Elena Kagan that most Republican senators followed the logic that led Obama, Schumer, and Clinton to oppose Roberts and Alito: that on the mostly hotly contested issues of our time, how these lifetime appointees vote matters more than how any senator — or any ten senators — votes.

The constitutional questions matter a great deal. So, to most politicians, do the practical results on everything from abortion to voting rights. A Supreme Court vacancy now must be treated with even greater urgency than a vacant Senate seat, especially when it swings control one way or the other.

Even a relative moderate, like Kennedy or Garland, must be viewed with utmost suspicion. Kennedy sided with conservatives on all their big 5-4 judicial victories this week. Garland would likely have turned these into 5-4 liberal wins, even if he is no Ruth Bader Ginsburg.

Once one party views things in these terms, both parties must do so or else practice unilateral judicial disarmament. Thus for every Merrick Garland, there is a Miguel Estrada.

That’s why Trump has an opportunity that eluded Reagan and both Bushes, to say nothing of every Republican president since World War II: to deliver the Supreme Court to conservatives for a generation.

Beyond that, it is all unpredictable.