WASHINGTON — With the retirement of Justice Anthony Kennedy and the likelihood that President Trump will choose a more conservative replacement, Chief Justice John Roberts Jr. is poised to play a pivotal role on the court he has headed for 13 years.

Roberts has been content to play the long game, moving the court to the right with incremental steps. But now, with more conservative colleagues on one side and liberals on the other, Roberts will have the ability to supply the deciding fifth vote and dictate the terms.

“With four presumably reliable conservative votes, he’ll be in a unique position to decide where, how far, and how fast, the court goes,” said Gregory Garre, who was a solicitor general under President George W. Bush. “This will put the chief in more of a swing justice role, and make him one of the most powerful chief justices in recent history.”