Republican U.S. Senate candidate Mehmet Oz greets supporters after the primary race on May 17, 2022 in Newtown, Pa.

Photo: Stephanie Keith/Getty Images

The votes in Pennsylvania aren’t all counted, and already President Trump is hinting that he might cry fraud if his endorsed candidate falls behind. On Wednesday his Senate pick, the TV doctor Mehmet Oz, led the GOP primary by roughly 2,500 votes. But some 105,000 mail ballots from both parties were yet to be tallied.

“Here we go again! In Pennsylvania they are unable to count the Mail-In Ballots. It is a BIG MESS,” Mr. Trump wrote on his Twitter knockoff, Truth Social. “Dr. Oz should declare victory. It makes it much harder for them to cheat with the ballots that they ‘just happened to find.’” On Thursday he added: “Stop FINDING VOTES in PENNSYLVANIA! RIGGED?” What a gent. This time the opponent Mr. Trump is discrediting happens to be a fellow Republican, David McCormick.

What’s more, it’s possible that Mr. McCormick might win in the end. Some of the areas with votes outstanding were expected to favor him. By Thursday morning Mr. Oz’s lead had fallen to about 1,200. Pennsylvania is notoriously slow to count mail ballots, in part because state law says they can’t be handled until the morning of Election Day.

If Mr. McCormick wins the final count, will Mr. Trump smear him as an election thief? Would GOP voters believe that nonsense? Pennsylvania has closed primaries, so everybody who voted for Mr. Oz or Mr. McCormick must be registered as a Republican.

By taking a political hatchet to Mr. McCormick, Mr. Trump could discourage Republicans from supporting him in November, giving away a winnable Senate seat. The Democratic nominee, John Fetterman, supports Medicare for All and would vote for whatever else Elizabeth Warren cooks up. Recall how Mr. Trump cost the GOP two Senate seats in Georgia’s 2021 runoffs.

Angry about his own loss, Mr. Trump told GOP voters not to trust the process. He helped the upset victories of Democrats Jon Ossoff and Raphael Warnock, which put the Senate in Democratic hands. That paved the way for President Biden’s $1.9 trillion Covid package, the ensuing 8.5% inflation, and a liberal Supreme Court Justice-in-waiting.

Don’t bet what’s left of your 401(k) on whether Mr. Trump has learned his lesson. His advice to Mr. Oz is also a warning about how Doug Mastriano, the GOP’s gubernatorial nominee, might react to a loss in the fall. Mr. Mastriano is the underdog against Democrat Josh Shapiro. If Mr. Mastriano falls short, will he and Mr. Trump claim it was due to some kind of massive coordinated fraud scheme that amazingly can’t be proved?

The Pennsylvania Legislature could help, but likely won’t, by passing a bill to let mail ballots be preprocessed a few days early, which many other states permit. Getting reliable results on election night is in the public interest, which is one reason we opposed H.R.1, the federal takeover of state election laws that Mr. Biden tried to demagogue through Congress.

GOP candidates are understandably eager to win Mr. Trump’s endorsement, but it could come with pressure to shout fraud when zero evidence for it exists. Whether Mr. Oz wins or loses, he would do his country a service if he publicly refused this turn toward conspiracy politics.