President Trump’s sole Republican primary challenger is calling on the commander-in-chief to step down.

“If Donald Trump is an American patriot, he should resign from office,” former Massachusetts Gov. Bill Weld wrote in an op-ed Wednesday appearing in The Bulwark, a conservative news and opinion website. Among the site’s founders is conservative commentator Bill Kristol, one of the leaders of the "Never Trump" movement.

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Weld – a vocal Trump critic who earlier this month launched a long-shot GOP primary challenge bid to unseat a president very popular within his own party – pointed to the findings in Special Counsel Robert Mueller’s Russia investigation report, claiming that Trump is a “one-man crime wave.”

“Time and again, Trump tried to use the power of the Oval Office to protect himself and his associates from the consequences of their actions. The only defense Trump has to obstruction of justice is that he was too incompetent to carry it off,” Weld argued. “Over the past two years, several Trump aides derailed his criminal conspiracies by distracting the president, or simply ignoring him. Trump’s failure to stop Bob Mueller does not negate how hard he tried.”

Weld spotlighted that the Mueller report “lifted up the rock and left Trump’s minions scurrying for cover. Already, five Trump associates have been convicted of serious crimes, including his former campaign manager, his longtime personal attorney, and his former national security advisor. And we don’t yet know the extent of criminality within the Trump campaign or the Trump White House because he Mueller report includes 12 criminal referrals that have been redacted to protect ongoing cases.”

And Weld claimed that “the American public, our international allies, the very rule of law itself would all be better served with a President Mike Pence.”

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The president on Wednesday once again declared the probe found “no collusion and they also came up with no obstruction,” adding: “I thought after two years we’d be finished with it, no—now the House goes subpoenaing. They want to know every deal I’ve ever done.”

And he pushed back against attempts by the Democratic majority in the House of Representatives to subpoena current and former White House officials in their probe.