The concern over Dr. Jackson’s nomination is bipartisan and emerged after Senate Veterans’ Affairs Committee interviews with more than 20 people, including current and former military personnel who had worked with him. The committee began an investigation last week into Dr. Jackson’s White House work record, and its Republican and Democratic leaders jointly announced Tuesday that his confirmation hearing, planned for Wednesday, would be postponed indefinitely “in light of new information presented to the committee.”

“We take very seriously our constitutional duty to thoroughly and carefully vet each nominee sent to the Senate for confirmation,” said Senators Johnny Isakson of Georgia, the committee chairman, and Jon Tester of Montana, its top Democrat, in a joint statement. “We will continue looking into these serious allegations.”

Dr. Jackson, speaking with reporters on Capitol Hill before meeting with a Republican senator Tuesday afternoon, gave no indication that he would withdraw his nomination. He also did not answer questions about the accusations.

But he added, “I’m looking forward to getting it rescheduled and answering everybody’s questions.”

Members of Mr. Tester’s staff said that they had been given several credible accounts of Dr. Jackson being intoxicated during official White House travel. In several cases, they said, he had apparently grabbed his medical bag and was “attempting to assert himself,” to show he was in charge.

On one trip during Barack Obama’s presidency, White House staff needed to reach Dr. Jackson for medical reasons and found him passed out in his hotel room after a night of drinking, Tester aides said. The staff members took the medical supplies they were looking for without waking Dr. Jackson.