Attorney General Jeff Sessions repeated the phrase “lock her up” during a speech to conservative high school students on Tuesday, chuckling as the crowd began a chant that Trump supporters used during the 2016 campaign to call for jailing Hillary Clinton.

Mr. Sessions, the country’s top law enforcement official, was speaking at a four-day conference hosted by the conservative organization Turning Point USA and attended by several hundred right-leaning high school students in Washington. In his speech, he sharply criticized American universities, saying they were coddling students and creating a “generation of sanctimonious, sensitive, supercilious snowflakes.”

When members of the audience began chanting “lock her up,” a common refrain at Trump rallies after the Republican candidate pledged to enlist a special prosecutor to investigate Mrs. Clinton, Mr. Sessions briefly strayed from his prepared remarks.

“Lock her up,” he said, laughing. “I heard that a long time over the last campaign.”

After pressure from President Trump, Mr. Sessions ordered senior prosecutors last year to evaluate various accusations against Mrs. Clinton and consider whether a special counsel should be appointed. Mr. Trump had asked on Twitter earlier that year why his “beleaguered A.G.” was not looking into “Crooked Hillarys crimes & Russia relations.” No such special counsel has been appointed.