Trump Ties Supreme Court Vacancy to Possible Disputed Election

President Trump wouldn’t commit to a peaceful transfer of power after the November election and predicted the outcome would be decided by the Supreme Court, a reason he wants to quickly fill the vacancy left by the death of Justice Ruth Bader Ginsburg.

“I think this will end up in the Supreme Court. And I think it’s very important that we have nine justices,” Mr. Trump said Wednesday.

During an event on social-media companies Wednesday, Mr. Trump amplified his long-running claim of widespread ballot fraud—which studies show is rare—and asserted...