(Bloomberg) -- Justice Brett Kavanaugh, who emerged Friday as the Supreme Court’s pivotal vote on abortion, said states outlawing the procedure may not bar residents from traveling to other states to terminate their pregnancies.

“May a state bar a resident of that state from traveling to another state to obtain an abortion?” he wrote in a concurring opinion. “In my view, the answer is no based on the constitutional right to interstate travel.”

Kavanaugh also said he didn’t believe a state could constitutionally impose liability or punishment for an abortion that took place before the court’s ruling Friday. He said that practice would violate either the Constitution’s due process clause or the ex post facto clause, which bars retroactive punishment.

He said those types of abortion-related legal questions “are not especially difficult as a constitutional matter.”

Kavanaugh’s vote is key because he joined with other conservative justices in the 5-4 ruling to overturn Roe v. Wade, the 1973 ruling that established abortion as a nationwide right. Without him, the court wouldn’t have a majority to uphold a law outlawing travel or one imposing retroactive punishment.

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