President Obama's contemplation of a military strike in Syria over its suspected use of chemical weapons has roused at least 170 members of Congress to question the constitutionality of such action, and others to urge caution informed by the quagmire of recent wars in Iraq and Afghanistan.

Few congressional voices, however, may be more resonant than those of the more than 100 military veterans in the House and Senate — particularly the 16 who served in the post-Sept. 11 conflicts in the Middle East, in both combat and non-combat roles.

If there's a single theme emanating from that mostly Republican class of members, it's one characterized by deep reticence — or flat out resistance — to the idea of military intervention without congressional authorization.

The potential that Syria possesses weapons of mass destruction "exists, and is certainly real," says Rep. Scott Perry (R-Pa.), an aviation battalion commander in Iraq, "and that's something service members can understand.

"But the president is going to have to persuade me. We've already let the world know we're coming, leaked the method of delivery, and even though we're hoping for regime change, what are we doing?"

Rep. Tammy Duckworth (D-Ill.), an Iraq veteran who lost her legs in the war, said this Thursday during a trip to Thailand:

"There's a real reluctance among American leadership, and myself especially, in committing our troops to another endless war that we don't know when it's going to end."

Even the most hawkish among the Iraq and Afghanistan vets aren't urging anything resembling the deployment of ground troops.

Many of the recent vets — including Perry and Rep. Tim Walz (D-Minn.), a retired Army National Guard command sergeant major — fault the Obama administration for squandering what they consider to be something-short-of-war opportunities over the past three years. In their view, he has failed to build an international coalition, or figure out how to work with difficult but necessary partners like Russia and China to address known atrocities in Syria.

"There have been options missed, opportunities left on the table," Perry says. "No service member wants to be involved in any operation that is ad hoc, that has no plan for success."

Walz, who, like most of his colleagues, is back in his southern Minnesota-based district meeting with constituents during the congressional summer break, says this about the run-up to an imminent strike: "There very well may be a plan and an end game, but it wasn't conveyed to Congress, and it wasn't conveyed to the American people."

The president's fateful August 2012 reference to a "red line" that would be crossed if the Assad regime used chemical weapons has also come in for harsh scrutiny, particularly among Republicans.

"If you're in a crowded theater and the only way to empty that crowded theater is if you yell the word 'red line,' don't do it," Rep. Adam Kinzinger (R-Ill.), an Air Force pilot in Iraq and Afghanistan who is currently on military duty with the Air National Guard, said at a late June hearing. "Because it has a very powerful meaning if you're president of the United States."

"I think the president drew red lines in the sand, and I think he did it prematurely," said Rep. Jim Bridenstine (R-Okla.), a combat pilot in Iraq and Afghanistan, and member of the Armed Services Committee, during a panel discussion this week. "The message he needs to understand is that his authorization to go to war does not come from the United Nations, it does not come from NATO, it does not come from any international organization. His authority comes from the United States Congress, and before we grant him that authority, he needs to define for us what our national security interests are, and so far he has not done that."

While the military will always carry out the commander-in-chief's mission, the veterans say, the point of the undertaking, and its end game, must be clear.

It isn't — not yet, they say, though they consider the administration's Thursday night conference call with congressional leaders a helpful development.

"I think the last 48 hours have been really productive," Walz, who served in Italy providing supply-line security during the Afghanistan War, said Friday morning. "There seems to be a slowing down, a thoughtfulness, a more deliberate attempt" to contemplate the road ahead.

"But I think the decision by the British House of Commons should alert people," he said, referring to the parliamentary vote Thursday against supporting the U.S. in military action in Syria.

"There was never a debate about the atrocious activities of [Syrian President] Bashar al-Assad," said Walz, who met Assad during a 2009 congressional trip to Syria. "This was about the constitutional way to go about it, so I know and so I can tell my constituents what we're doing."

Among Republicans, Obama faces an additional hurdle. The president's credibility with many recent veterans, explained Perry, the Pennsylvania congressman, is compromised by his past criticism of President George W. Bush's actions and rationale in going to war in Iraq.

"I do think this adds a dimension of hypocrisy," Perry said. "Quite honestly, I don't think the president has any moral high ground, based on his past rhetoric."

Back in 2007, when Obama was an Illinois senator seeking the Democratic presidential nomination and Bush was considering a military strike in Iran, Obama staked out this unequivocal position to The Boston Globe: "The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation ... History has shown us time and again, however, that military action is most successful when it is authorized and supported by the legislative branch. It is always preferable to have the informed consent of Congress prior to any military action."

Liberal members of Congress have joined their more conservative colleagues noting that both Obama, whose opposition to the Iraq war helped pave his way to the White House, and Vice President Joe Biden were strident in their assertions that the Constitution does not provide the president with authority to take military action without a direct threat to the nation.

"The president's powers are there for emergencies, when American lives are being threatened," says Rep. Brad Wenstrup (R-Ohio), who was a combat surgeon in Iraq and is a member of the House Armed Services Committee. "A majority of Congress is not informed to the level they would like to be to make a decision. I certainly would want to truly verify that the president's red line had been crossed, especially since Assad is telling the world they've done no such thing."

How many lives will be jeopardized, he asked, how many relationships with allies will be undermined?

Walz, the Minnesota Democrat, described his qualms about the prospect of military strikes this way.

"I'm not sure that having served in the military brings you a special insight — we're all products of our past. But this is very visceral for members who have served. There's a very strong desire that the end game in this is well thought out. It can't be haphazard. The military will execute it, but the civilians better get the mission right."

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