The biggest cases of the Supreme Court term so far have a surprising common thread. On a court with five Republican appointees, the liberal justices have been in the majority in rulings that make workplace discrimination against gay and transgender people illegal, protect young immigrants from deportation and, as of Monday, struck down a Louisiana law that restricted abortion providers.

As surprising, Chief Justice John Roberts, a conservative nominated by President George W. Bush who has led the court for nearly 15 years, has joined his liberal colleagues in all three. Since the retirement of Justice Anthony Kennedy in 2018, Roberts has played a pivotal role in determining how far the court will go in cases where the court's four liberals and four conservatives are closely divided.

Here's a look at where Roberts stood in the abortion, immigration and LGBT cases, his history on the court and what's at stake in coming decisions in which Roberts could play a key role:

On Monday, Roberts joined liberal justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan in striking down Louisiana's Act 620. The justices ruled that the law requiring doctors who perform abortions to have admitting privileges at nearby hospitals violates the abortion rights the court first announced in the landmark 1973 Roe v. Wade decision.

But Roberts' reason for siding with the liberals had less to do with his feelings on abortion than with his feelings on whether the court should do an abrupt about-face. Four years ago the court's four liberal members and Justice Kennedy struck down a Texas law nearly identical to Louisiana's. At the time, Roberts was a vote in dissent. But with Kennedy's retirement and replacement by conservative Justice Brett Kavanaugh, many conservatives had hoped the result in the Louisiana case would be different. Not so, Roberts wrote: “The result in this case is controlled by our decision four years ago."