the Senate’s Republican campaign chief on Thursday appeared to escalate an ugly quarrel with the party’s longtime leader in the chamber, Senator Mitch McConnell, in the latest sign of the G.O.P.’s eroding confidence about winning back the majority in November.

Without naming Mr. McConnell, Senator Rick Scott of Florida, the chairman of the National Republican Senatorial Committee, lashed out in a blistering opinion piece in The Washington Examiner at Republicans he said were “trash-talking” the party’s candidates, an apparent reference to comments last month in which Mr. McConnell said that “candidate quality” could harm the G.O.P.’s chances of retaking the Senate. Mr. Scott called such remarks “treasonous” and said those who make them should “pipe down.” 

“Unfortunately, many of the very people responsible for losing the Senate last cycle are now trying to stop us from winning the majority this time by trash-talking our Republican candidates,” Mr. Scott wrote. “It’s an amazing act of cowardice, and ultimately, it’s treasonous to the conservative cause.”

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Speaking to reporters in his home state last month, Mr. McConnell conceded that Republicans had a stronger chance of winning back control of the House than the Senate in November.

“Senate races are just different — they’re statewide, candidate quality has a lot to do with the outcome,” he said at a Chamber of Commerce lunch in Florence, Ky. The comment was widely interpreted to reflect Mr. McConnell’s growing concern about Republicans’ roster of Senate recruits, which includes several candidates who have been endorsed by former President Donald J. Trump and appear to be struggling in competitive races.