WASHINGTON -- As bombs dropped over Syria Monday evening, marking the beginning of a U.S.-led effort to eradicate the Islamic State in that country, most members of Congress were back at home.

The legislative branch adjourned its business at the end of last week to tend to elections. In doing so, it left unresolved the issue of authorizing the war that President Barack Obama would start days later. Congressional inaction didn't upend the White House's plans; the administration had already claimed it had legal authority to launch such strikes in Syria.

But by leaving town before the president started operations, lawmakers may have done serious harm to their own institution, Sen. Tim Kaine (D-Va.) argued in an interview with The Huffington Post. Not only had they diminished the standing of Congress with respect to the executive branch, they also may have given unintended consent to a Dick Cheney-like vision of presidential war powers.

"[Congress has] sort of allowed the Cheney pre-emptive war doctrine to exist by another name," Kaine said. "In this instance, they allowed the president to say, 'ISIL [the Islamic State] is the bad guys, and I can go after them even though there has been testimony that they pose no imminent threat of attack on the United States.' If the president just gets to do this without Congress, then we will be embracing the Cheney pre-emptive war doctrine, which I think is just brutally wrong."

Kaine, one of the most outspoken advocates for passing a new authorization for use of military force, spoke just hours before word broke of the first airstrikes in Syria. He is slated to give a larger address on Tuesday at the Obama-allied Center for American Progress, speaking against the legal underpinnings for expanded military operations.

Two weeks ago, he was something of a lone voice in the Senate on this matter. While other lawmakers agreed with the basic idea that the president needed to come to Congress to authorize airstrikes in Syria, few were willing to badger the point. During a meeting in the White House a few weeks ago, the president told congressional leadership that he believed the 2001 Authorization for Use of Military Force covered such operations. Senate Minority Leader Mitch McConnell (R-Ky.) pushed back -- but only gently, and hardly in a way that would have prevented the president from acting before Congress did.

Since then, more lawmakers have come around to Kaine's position, but not a critical mass of them. Both chambers voted to send $500 million to train and aid moderate Syrian rebels. (Kaine voted in favor of the measure as well.) But lawmakers left town before considering an authorization for U.S. air operations, and aren't expected back until after the November elections.

"I think the damage would be enormous," Kaine said of the possibility that Congress may never actually take a vote. "It is highly immoral to ask servicemen and women to risk their lives around a mission if the president feels that it is inconvenient to ask Congress to bless it, or members of Congress are afraid of the political consequence of blessing it."

Hoping to avoid total abdication of responsibility, Kaine has introduced his own authorization for use of force, as have others in Congress. His hope is for a more narrowly defined proposal that would be specifically tailored to dealing with the Islamic State in Iraq and Syria, and would have a sunset provision. The idea is not to pass anything that could be used by subsequent administrations to justify subsequent -- tangentially related -- military activity.

That was part of the problem with the 2001 AUMF, Kaine said. It needed to be narrowed and "maybe ultimately repealed." The president said as much at a speech at the National Defense University in 2013. Instead, the AUMF was used by the Obama administration as a basis for action in Syria.

"Well, they are [using it], which I'm disappointed in," said Kaine. "I think it is being used for purposes that were clearly beyond its original intent, and we need to refine it."

Kaine said he's confident that an updated authorization -- whether his own or another lawmaker's -- will get consideration once Congress returns for the lame duck session. He said he has gotten assurances from leadership that "we will have a vote," though a Senate Democratic aide told The Huffington Post that such a declaration is premature. Senate Majority Whip Dick Durbin (D-Ill.) has pledged that there will be a debate.

Looming over the issue of votes and timing is that the president has already acted, prompting several lawmakers on Tuesday to urge leadership to reconvene Congress and hold a vote.

.@SpeakerBoehner shld bring Members back to debate/vote on AUMF that supports current mission but ensures no ground troops. No Iraq War 2.0 — Chris Van Hollen (@ChrisVanHollen) September 23, 2014

But the wheels of military action are in motion, not just operationally but also legally. As the New York Times recently reported, Congress could end up providing a de facto authorization for the president's airstrikes by not explicitly voting them down. Put on notice about Obama's legal justification for launching the strikes, their inaction could be interpreted as a ratification.