When he ran against Donald J. Trump in 2016 for the Republican presidential nomination, Senator Rand Paul of Kentucky quipped that “a speck of dirt would make a better president” than the bombastic businessman from New York.

Then came President Vladimir V. Putin of Russia, his government’s interference in a White House campaign in which Mr. Paul barely made a ripple, and last week’s presidential summit meeting in Helsinki, Finland, which pretty much everyone but Mr. Paul deemed a diplomatic disaster.

Suddenly, in the mind of the junior senator from Kentucky, Mr. Trump has soared from lower than that speck of dirt to high enough for Mount Rushmore.

“The hatred for the president is so intense that partisans would rather risk war than give diplomacy a chance,” Mr. Paul fumed on the Senate floor last week in a long defense of Mr. Trump’s Helsinki meeting. “This is crazy.”