When 14 Senate Republicans joined every Democrat in voting last month to end U.S. military support for the Saudi-led coalition fighting in Yemen, Sen. Tim Kaine (D-Va.) heard more than a rebuke of the Trump administration’s policy.

He interpreted the vote to mean lawmakers are increasingly interested in holding the president to account regarding the use of military force and could be persuaded to update the current authorization for the use of military force, one of Kaine’s signature issues.

The recently reelected senator wants to replace post-9/11 authorizations Congress passed in 2001 and 2002 as a legal basis for military action in Iraq and Afghanistan. He said the legislation has been inappropriately stretched to justify U.S. military engagements well beyond the original authorization.

Kaine said Congress has abdicated its responsibility for declaring war under the Constitution, and a new Authorization for Use of Military Force (AUMF) would show troops risking their lives that Congress had made a fresh determination that their mission was in the national interest.

The United States has used those early authorizations in 37 instances to send forces to 14 nations, including Libya, Turkey, Georgia, Syria, Iraq, Afghanistan, Yemen, Eritrea, Ethiopia, Djibouti, Somalia, Kenya, the Philippines and Cuba, according to Kaine’s office.

“The height of public immorality is to order troops into war without Congress having the guts to vote on it, and that has been my feeling for a very long time,” Kaine said in a recent interview.

Kaine has made little progress on the issue since arriving on Capitol Hill in 2013, and he returns to Congress in January without the three Republicans who have been important allies on the issue: Sen. Bob Corker (R-Tenn.), chairman of the Foreign Relations Committee, and Sen. Jeff Flake (R-Ariz.) are retiring from Congress, and Sen. John McCain (R-Ariz.) died in August.

Earlier this year, Kaine and Corker led a bipartisan group of senators in releasing a proposal for a new AUMF covering operations against al-Qaeda, the Taliban, the Islamic State and affiliated groups.

Kaine argues that the worsening humanitarian crisis in Yemen and the killing of Washington Post contributing columnist Jamal Khashoggi by Saudi agents in October means more senators are paying attention to the cost of U.S. involvement in conflicts around the world.

If lawmakers were willing to take a first step toward rebuking the president over Yemen, Kaine argues, perhaps more will be willing to support his fight to update the authorizations on which the Trump administration has been relying.

With control of the House in their hands, he said, Democrats could pass a narrow resolution. Although the majority-Republican Senate would be likely to find it too restrictive, such a resolution could provide a starting point for Kaine to craft a compromise acceptable to 60 senators.

The Nov. 28 procedural vote to take up a resolution, drafted by Sens. Bernie Sanders (I-Vt.) and Mike Lee (R-Utah), passed, 63 to 37. Eight months earlier, a vote to advance the same resolution failed, 44 to 55.

The latest vote “demonstrates a strengthening commitment to the constitutional order on war declaration and a level of concern about the Saudis’ getting just a free pass to do whatever they want,” Kaine said.

The issue is important to him as a senator from a military-heavy state and the only senator with a child on active duty in the military.

Kaine remarked on what he said was a surreal aspect of his 2016 campaign for the vice presidency. He found himself running against a ticket headed by Donald Trump, who he said was actively seeking Russia’s help to defeat Hillary Clinton, while Kaine’s son, a U.S. Marine, was deployed and training allies of the United States to protect themselves against Russia.

“There was an Alice in Wonderland character to all that, to both of those things happening at the same time,” Kaine said.

The senator’s interest in war powers dates to 2002, when, as lieutenant governor, he drove around Virginia and heard radio reports about Congress rushing to authorize war in Iraq before that year’s midterm elections, a move he said he considered a political stunt. A few years later, he read a report on war powers from the Miller Center at the University of Virginia and kept it in hopes of one day teaching a class on the subject.

Instead, he went on to serve as governor and then was elected to the Senate. Although he considers Barack Obama a friend, he said, he pressed the former president to seek permission from Congress before committing U.S. forces to the conflict in Libya.

Kaine said he worried at the time that the next president might not be as restrained in the use of military power.

Enter Trump, who has threatened to initiate military action against Syria, Iran and North Korea.

“This president has a very dangerous belief that he doesn’t need Congress for anything and he can do whatever he wants,” Kaine said. “When it comes to war making, I think that should scare everybody.”