Senate Majority Leader Mitch McConnell joined Donald Trump Tuesday in warning that an independent candidate’s entry into the presidential race could help swing the election to the Democrats, after Weekly Standard editor Bill Kristol stirred the pot by predicting another contender would join the field.

“That can only help elect Hillary Clinton,” the Republican leader told Fox News’ “Fox & Friends.”

He said Trump, now the presumptive Republican nominee, won the primary “the good, old-fashioned way … and we ought to respect the wishes” of GOP voters.

“I think anything that divides this sort of right-of-center world is not helpful, and I don’t think it’s a good idea to do anything that helps us elect Hillary Clinton,” McConnell said Tuesday.

Trump and Kristol were engaged in a personal Twitter battle over the long weekend regarding the prospect of another candidate entering the race.

Kristol kicked off the speculation, and the backlash, when he claimed Sunday: “There will be an independent candidate -- an impressive one, with a strong team and a real chance.”

Kristol, along with other conservative pundits, long has been working to attract an independent candidate to run in November amid lingering concerns in some wings of the Republican Party about Trump’s conservative credentials. This effort to date has struggled to recruit a willing candidate, while running into logistical hurdles -- including the rules and deadlines for getting new names on the ballot.

Kristol’s latest prediction prompted Trump to warn that the mystery candidate could act as a “spoiler” in November.

Kristol fired back on Monday, mocking Trump over his reaction.