“Mr. President, release your tax returns or shut up,” he said at one point, looking directly into the assembled cameras.

And Mr. Biden, who often talks about civility, appeared far more eager to seize opportunities to tweak his Democratic rivals than he has on many previous occasions.

“God love Bernie, you know it was really good, I really mean it, to see him so healthy and moving last night,” Mr. Biden said of Mr. Sanders, who recently suffered a heart attack. “ But Bernie! Bernie doesn’t pay for half his plan.”

Asked about Ms. Warren’s remark at the debate, that the United States should “get out of the Middle East,” Mr. Biden, a former chairman of the Senate Foreign Relations Committee, embraced the chance to attempt to draw another contrast .

“I quite frankly was surprised,” he said. “I have never heard anyone say, with any serious background in foreign policy, that we pull all troops out of the Middle East. ”

Ms. Warren’s campaign has clarified that she was referring to combat troops.

Later Wednesday, Mr. Biden gave a foreign policy address in Iowa where he briefly referenced that moment, again noting his surprise at her remarks before turning back to his foreign policy agenda.

To some extent, Mr. Biden’s attack is part of a broader effort to cast himself as uniquely qualified on foreign policy, an argument he made explicitly in his speech in Iowa.