McConnell says ‘loony lies’ spread by Marjorie Taylor Greene are a ‘cancer’ on G.O.P.

Senator Mitch McConnell said on Monday that the “loony lies and conspiracy theories” embraced by Representative Marjorie Taylor Greene amounted to a “cancer” on the Republican Party, issuing what in effect was a scathing rebuke to the freshman House Republican from Georgia.

In a statement reported by The Hill, Mr. McConnell of Kentucky, the minority leader, never named Ms. Greene, but he referred to several of the outlandish and false conspiracy theories she has espoused and warned that such statements were damaging the party.

“Somebody who’s suggested that perhaps no airplane hit the Pentagon on 9/11, that horrifying school shootings were pre-staged, and that the Clintons crashed JFK Jr.’s airplane is not living in reality,” Mr. McConnell said. “This has nothing to do with the challenges facing American families or the robust debates on substance that can strengthen our party.”

House Republican leaders in the past week have been mostly silent as pressure mounted to respond to the cascade of Ms. Greene’s problematic social media posts and videos that have surfaced in the past week, in which she endorsed a seemingly endless array of conspiracy theories and violent behavior, including executing Democratic leaders. At the same time, they are weighing calls within their ranks by loyalists of former President Donald J. Trump to strip Representative Liz Cheney, the No. 3 Republican, of her leadership post as punishment for her vote to impeach Mr. Trump.

In a separate statement reported by CNN, Mr. McConnell weighed in on behalf of Ms. Cheney, who represents Wyoming’s sole congressional district, calling her “a leader with deep convictions and the courage to act on them.”

Mr. McConnell, who is said to believe that Mr. Trump committed impeachable offenses, has made it clear he is open to voting to convict the former president for “incitement of insurrection,” although he voted with the vast majority of Republicans last week to dismiss the case as unconstitutional.

The twin statements by Mr. McConnell amounted to a rare step by the most powerful Republican in Washington to insert himself into an increasingly ugly intraparty feud.

They have intensified pressure on Representative Kevin McCarthy of California, the minority leader, who is to meet with Ms. Greene later this week amid calls from outside Republican groups and some members of his own party to revoke the Georgia freshman’s committee assignments. This leaves Mr. McCarthy on an uncomfortable middle ground after Ms. Greene over the weekend said she spoke with Mr. Trump and received his support, essentially framing any action Republican leaders might take against her as defying him by proxy.

Ms. Greene offered her own retort in response to Mr. McConnell on Twitter, saying “the real cancer” on the party was “weak Republicans who only know how to lose gracefully.”

House Democrats on Monday indicated that they were prepared to unilaterally remove Ms. Greene from her committees if Mr. McCarthy does not act, advancing a measure to strip her of assignments that will be considered by the House Rules Committee on Wednesday.