MOSCOW — There may be little that pleases Senator Rand Paul, the libertarian-leaning Kentucky Republican, more than thumbing his nose at Washington groupthink.

So it was on Monday when Mr. Paul, decamping for the Senate’s one-week recess, took his lonely defense of President Trump’s Russia policy to Moscow to deliver a show of contrarianism all too familiar to his colleagues back home.

“I’ve traveled here to say that there are many Americans who want to have diplomacy, that want to have engagement; I’m one of them,” Mr. Paul said, standing beside Konstantin Kosachyov, the chairman of the foreign relations committee of Russia’s senate who has been subject to American sanctions since April.

At home, Mr. Paul’s fellow senators speak in grave tones about how to respond to an alarming pace of revelations about the scope and durability of Russia’s campaign to undermine the democratic process — an effort that American intelligence officials warn remains active despite American retaliation. One plan, introduced last week by three Republicans and three Democrats, calls for “crushing” new sanctions.