Sen. Tim Kaine (D-Va.) introduces Hillary Clinton before her concession speech at the New Yorker Hotel’s Grand Ballroom in New York City on Nov. 9. (Olivier Douliery/European Pressphoto Agency)

In his first floor speech since he and Hillary Clinton lost the election, Sen. Tim Kaine (D-Va.) revived one of his signature issues Wednesday: urging Congress to authorize military force against the Islamic State terrorist group.

Since Congress declared war against the 9/11 attackers, he said, Presidents George W. Bush and Obama expanded the definition to justify using military force in 14 nations — and set a dangerous precedent for President-elect Donald Trump.

He called lawmakers’ unwillingness to vote on new conflicts in Syria, Turkey, Yemen and other countries the “height of public immorality” and disrespectful to the troops.

In the 15-minute speech, Kaine, himself the father of a Marine, paid tribute to Senior Chief Petty Officer Scott C. Dayton, of Woodbridge, Va., whose death last week marked the first U.S. combat casualty in Syria.

“We shouldn’t order people into harm’s way to risk their lives unless there’s a political consensus,” Kaine said.

As Kaine shifts from running for vice president back to freshman senator, he has reprised his role as a moral guide for the body and said the time is right to take a fresh look at the war powers issue.

He urged his colleagues to review the progress of wars against terrorist organizations, redraft the 2001 authorization and reassert Congress’s place in the debate.

Eighty percent of the members of Congress were not in office in the days after the Sept. 11, 2001, attacks and have never had an opportunity to debate the war against the Islamic State, which he noted did not exist until two years later, he said.

Despite sharing a ticket with Clinton, a former secretary of state, and being an early endorser of Obama in 2008, Kaine has split sharply with the current administration on the issue.

Of all the powers of Congress, he said, “I can’t think of any that are more important than the power to declare war.”

After the weapons of mass destruction justification for the Iraq War dissolved under Bush, Kaine acknowledged that lawmakers may be reluctant to go on the record with votes on various conflicts. “It’s a backbone issue,” he said in an interview after the speech.

In addition, he said, Trump and his colleagues must grapple with difficult questions about what it means to declare war against a terrorist group that doesn’t follow the Geneva Conventions’s war protocols.

“We’ve drifted as if the challenge would solve itself,” he said. “It’s not going to.”

Kaine is a member of the Senate Armed Services and Foreign Relations committees.