Senator Rand Paul of Kentucky, who in recent weeks has had to explain how Wikipedia entries came to be incorporated into his speeches with no attribution, faced charges of direct plagiarism on Monday night.

In an op-ed article he wrote for The Washington Times in September on mandatory minimum prison sentences, Mr. Paul, a Republican, appears to have copied language from an essay that had previously run in The Week magazine.

That article, written by Dan Stewart, an editor for The Week, included this sentence: “America now jails a higher percentage of its citizens than any other country, including China and Iran, at the staggering cost of $80 billion a year.” It was posted to the web on Sept. 14.

On Sept. 20, Mr. Paul wrote this: “America now jails a higher percentage of its citizens than any other country, including China and Iran, at the staggering cost of $80 billion a year.”