WASHINGTON — One after another, Democrats on the Senate Judiciary Committee pressed Attorney General Jeff Sessions to provide information. And again and again in nearly five hours of testimony on Wednesday, Mr. Sessions refused.

The lawmakers asked for more details about his conversations with President Trump before he fired James B. Comey, the former F.B.I. director, and pardoned Joe Arpaio, the former sheriff in Arizona. They wanted to know what the two had discussed about Robert S. Mueller III, the special counsel investigating Russia’s interference in the 2016 election and possible links to Mr. Trump.

The senators also asked about topics not involving the president, like whether Mr. Sessions had conversations with the attorney general of Texas about an immigration program the state had threatened to sue over, and whether any evidence supported Mr. Trump’s claim that the Cuban government was behind sonic attacks on American diplomats.

“I’m just not able to comment,” Mr. Sessions said.

Mr. Sessions’s demurrals — and Democratic anger over them — were a recurring theme during his first appearance before the panel for an oversight hearing in the eight months since he became the nation’s top law enforcement officer.