John Roberts is likely about to occupy a dual position that no one else has in the modern history of the United States: He will be both the court’s chief justice and, with the retirement of Justice Anthony Kennedy, its median voter — the person in charge of the court, and the justice most likely to swing a decision one way or the other. This combination of institutional power and ideological centrality will give Roberts remarkable sway over the business and decisions of the court, and by extension the law of the land, possibly for decades to come.

But liberals cannot reasonably hold out much hope that Roberts will sway votes for some of their favored causes the way Kennedy did. While the statistical metrics show Roberts taking a relatively moderate position, he has very rarely voted with the liberals when it mattered.

Roberts, 63, took his seat on the bench in 2005, after then-President George W. Bush appointed him. Like Kennedy, he has proven solidly conservative on major American issues such as voting rights, campaign finance and gun control. Unlike Kennedy, Roberts dissented in the case that legalized gay marriage, dissented in the case that found executing an intellectually disabled person to be unconstitutional, and dissented in the case that affirmed that California must reduce its overcrowded prison populations, to name but a few examples.

Roberts usually voted conservative in close cases Percentage of votes coded as conservative in each justice’s Supreme Court career, through the 2016 term All cases Close cases justice Total Conservative rulings Percent conservative Total Conservative rulings Percent conservative Thomas 1,918 1,270 66.2 427 342 80.1% Scalia 2,461 1,566 63.6 583 472 81.0 Alito 768 485 63.2 182 153 84.1 O’Connor 2,484 1,483 59.7 567 419 73.9 Roberts 800 463 57.9 188 155 82.4 Kennedy 2,361 1,344 56.9 537 383 71.3 Breyer 1,624 675 41.6 379 81 21.4 Souter 1,497 594 39.7 337 60 17.8 Kagan 427 164 38.4 94 17 18.1 Stevens 3,515 1,335 38.0 798 178 22.3 Ginsburg 1,727 645 37.3 395 58 14.7 Sotomayor 523 193 36.9 109 11 10.1 “Close cases” are those decided by any five-justice majority, not exclusively 5-4 decisions. The 2016 term ended in September of 2017. Source: supreme court database

Despite his conservative pedigree, Roberts’s ideology has been slipping left in recent years according to the most prominent measure of such things, called Martin-Quinn scores. By this measure, he’s the most moderate conservative remaining on the court, and with President Trump expected to appoint another firm conservative, Roberts will probably remain the only member of the court’s right-wing bloc who approaches a centrist position.

But has Roberts ever really swung? Will he swing in the future?

Roberts has been involved in 800 decisions while on the high court bench, according to Washington University School of Law’s Supreme Court Database. In 313 of these, he voted with the majority in a decision that the database describes as “liberal,” as coded by the database’s maintainers, a group of legal and political science scholars. (Occasionally cases have more than one ideology coding. If any code for a case was liberal, we’ve included the case in this tally.) In only 15 of those cases, however, was Roberts’s vote pivotal. That is, there were only 15 instances in which Roberts voted with the majority in a 5-4, liberal-leaning decision, where switching his vote would also have switched the ruling to a conservative one. What do you call a swing justice who doesn’t swing?

And we can winnow this short list down even further. In some of these 15 “liberal” cases where Roberts’s vote was pivotal, the chief justice actually joined the typically conservative bloc of voters — Clarence Thomas, Antonin Scalia, Samuel Alito and Kennedy. This is because the database’s definition of “liberal” does not always follow the conventional meaning of the word — in certain technical cases decided by the court, there’s not necessarily a clean distinction between which position is “liberal” or “conservative” as we commonly understand those words. When we get rid of those cases where he sided with at least two members of the conservative bloc, the list of Roberts’s liberal “swings” drops to five cases. Five liberal-leaning decisions where Roberts joined his liberal colleagues and actually changed the outcome by doing so. They cover a small grab bag of topics and, with one big exception, aren’t exactly the sorts of results that show up in your phone’s push alerts.

The first of these five, and Roberts’s most famous “liberal-leaning” vote, came in 2012, when he wrote the opinion that upheld the Affordable Care Act. That case, called National Federation of Independent Business v. Sebelius, found the ACA’s individual mandate, which imposes fines on certain people who do not carry health insurance, to be a constitutional use of Congress’s power of taxation. Roberts performed some jurisprudential contortions to arrive at his opinion, and the result was seen as an expression of his desire to maintain the credibility and legitimacy of the court.

The second, Michigan v. Bay Mills Indian Community, came in 2014. It concerned Native American tribes’ sovereign immunity and a state’s lawsuit to stop a recognized tribe from operating a small casino. The court ruled in favor of tribe. Dart Cherokee Basin Operating Company v. Owens, also decided in 2014, was a legally technical case about the procedure for removing a case from state court to federal court. Yates v. United States was a case decided in 2015 and famous for its fish — specifically, whether a fish was a “tangible object” as defined by a certain provision in the federal criminal code. The court found that, in this case, a fish was not a tangible object. And finally, Williams-Yulee v. The Florida Bar was a 2015 free speech case concerning money in politics. Specifically, Roberts and the four more liberal justices found that the First Amendment did not prevent states from barring judicial candidates from soliciting funds for their campaigns.

Aside from the Obamacare case, these aren’t the sort of front-page rulings that liberals crave.

So what about Roe v. Wade, possibly the court’s most famous case and currently its most discussed? In his confirmation hearing, Roberts repeatedly expressed his desire to “stay away from a discussion of particular cases.” Neil Gorsuch, Trump’s first appointee, also took this tack. “As a nominee, it would not be proper to speculate about hypothetical contingent events,” he said. Whomever Trump nominates will likely adopt a similar tactic during the confirmation process, and Trump has said his advisers warned him against explicitly discussing Roe with his would-be nominees. “They’re all saying, don’t do that, you don’t do that, you shouldn’t do that. But I’m putting conservative people on.” However, much of the shortlist Trump is expected to pull from was vetted and approved by the conservative Federalist Society, and few people, it has been reported, are more dedicated to overturning Roe than that group’s executive vice president, Leonard Leo.

But Roberts has also discussed the importance of the legal idea of stare decisis — “to stand by things decided.” And Roberts, especially as the chief justice, is deeply concerned with the credibility and legitimacy of the institution of the Supreme Court. (That said, Roberts has been willing to overturn major precedent at times, including this term in a case about public-employee unions.) Whether Americans view the Supreme Court favorably is already a partisan issue. Any decision overturning Roe — a 45-year-old precedent that two-thirds of voters want to remain in place — would likely be made by a 5-4 majority that includes a justice appointed after Republican senators’ stonewalling prevented a Democratic nominee from getting a confirmation hearing, and all that combined divisiveness may be too sharp a challenge to the legitimacy Roberts so hopes to protect.

Amelia Thomson-Deveaux contributed research to this article.