The Senate majority leader, Mitch McConnell, would not rule out the possibility of rescinding his endorsement of Donald J. Trump’s presidential bid down the road, and he described the candidate as lacking knowledge in a number of areas in an interview released on Friday.

The comments from Mr. McConnell, in an interview with the “Masters in Politics” podcast on Bloomberg Politics, came as Republicans down the ballot continue to face questions about Mr. Trump’s criticism of the Indiana-born federal judge overseeing a case against Trump University as “Mexican.” Mr. McConnell has been pointed in his criticism of those remarks.

It was the first time, though, that Mr. McConnell offered anything less than an ironclad response of sticking with Mr. Trump, despite the numerous controversies that the presumptive Republican nominee has instigated.

Asked if there was a line that Mr. Trump could cross that would prompt Mr. McConnell to rescind his endorsement, Mr. McConnell demurred.