WASHINGTON ― After President Donald Trump launched a Tomahawk missile strike on a Syrian airfield, the debate among congressional Democrats was not over the actual merits of bombing Syrian airfields but instead about Trump’s decision process.

The reaction of Sen. Bernie Sanders (I-Vt.), the most progressive member of the Senate Democratic caucus, was a case in point.

“It is very questionable whether it is legal” to bomb the Syrian air force without congressional involvement, Sanders told The Huffington Post.

Some of Sanders’ colleagues were less equivocal, including Sen. Chris Murphy (D-Conn.), who said this “certainly is not a lawful act.” On the other end of the spectrum, Sen. Ben Cardin (D-Md.) said it “seems like a reasonable exercise of presidential power.”

But only a handful of Democrats questioned the evidence that Syrian President Bashar Assad used chemical weapons on civilians, the efficacy of using force to address that crime or the overall pattern of U.S. involvement in the Middle East.

The relatively measured criticism from top Democrats reflects a complex array of factors that have again put the party out of step with some grassroots members. In many cases, Democratic lawmakers simply agree with the need to punish Assad for using chemical weapons on the town of Khan Sheikhoun, even as they are uneasy about Trump’s leadership, the legality of his actions or the consequences of a strike.

Carlos Barria / Reuters President Donald Trump, right, sits by Secretary of State Rex Tillerson at a meeting with China's President Xi Jinping in Florida the day after Trump ordered missile strikes on an air base in Syria.

That leaves Democrats in an interesting political position. For months they have taken every opportunity to lambaste Trump as a threat to the very fabric of the American republic. And from Trump’s travel ban to the Obamacare replacement debacle, the strategy has largely paid off. Now, with Trump launching the first direct attacks on the Syrian government, Democrats are more ambivalent.

Larry Korb, a senior fellow at the Democratic-aligned Center for American Progress, said he was “not surprised” that Democrats were sympathetic to the idea of a retaliatory airstrike. Many Democrats subscribe to a “responsibility to protect” doctrine that swift force is justified to prevent major humanitarian catastrophes, according to Korb.

Democrats should be more concerned, Korb said, with the prospect of this leading to more significant U.S. intervention in Syria.

“The real question is: What comes next?” said Korb, who supported the Obama administration’s decision not to heed calls to arm Syrian rebel groups more aggressively or remove Assad by force.

The fact that Democrats may have substantial reasons to embrace the idea of retaliating against Assad does not diminish the divide between many elected leaders and the ardent anti-interventionism of the party’s base.

“My expectations [of Democrats] were very low, and my expectations were met,” said Phyllis Bennis, a foreign policy expert at the left-wing Institute for Policy Studies. “Am I disappointed that we don’t have an antiwar party? Yes, I am.”

Bennis represents a wing of the peace camp that believes military force, whether legal or not, is justified only in very limited circumstances of self-defense. The last U.S. intervention she considers “legitimate” was World War II.

Bennis and other progressive critics argue that there should be a full international investigation of the use of chemical weapons to determine definitively whether Assad is responsible, which they admit is extremely likely.

“Having a full investigation is not some sort of delaying tactic. It is essential to getting real accountability,” said Stephen Miles, director of the progressive Win Without War coalition.

The residue of the decision not to bomb in 2013 created an environment where the next time it happened, a strike was going to be a foregone conclusion. Steven Simon, former National Security Council official

That view got a high-profile boost from Canadian Prime Minister Justin Trudeau, who urged caution in an interview with The Globe and Mail on Thursday. Trudeau called for a United Nations Security Council resolution that will enable the world “to determine first of all who was responsible for these attacks and how we will move forward.”

Even if Assad’s guilt is established, punishing him militarily would not be an effective response, according to Miles of Win Without War. He supports removing the weapons from Syria, negotiating a diplomatic end to the war and trying alleged war criminals.

“The ultimate accountability comes from international tribunals,” Miles said. “It is really gratifying to blow things up, but that doesn’t make it accountability.”

But Win Without War, Credo, MoveOn.org and Peace Action, which jointly condemned Trump’s strike as a “reckless act of war,” have largely mirrored Democrats’ talking points about the strikes’ legality in their mobilization strategy.

A petition Credo is circulating that quickly picked up over 57,000 signatures calls on Democrats to “rein in Donald Trump’s unauthorized military strikes and hold immediate emergency deliberations on Trump’s illegal escalation of military engagement in Syria.”

Miles praised House Minority Leader Nancy Pelosi (D-Calif.) for demanding that Congress reconvene to debate a new authorization for use of military force ― and saved his criticism for Democratic lawmakers, including Senate Minority Leader Chuck Schumer (D-N.Y.), who voiced unreserved agreement with Trump’s decision.

“It’s not the first time we have seen Democrats in Congress who are way out of touch with where their base is,” he said.

Bloomberg/Getty Images Sen. Bernie Sanders (I-Vt.) has questioned the legality of President Trump's Syria strikes but not their fundamental merits.

Democrats have often chafed under Republican claims that they are weak on national security. After the terrorist attacks of Sept. 11, 2001, critics saw signs of this insecurity in the ease with which Democratic lawmakers lined up behind then-President George W. Bush’s invasions of Afghanistan and Iraq.

But veteran Democratic foreign policy thinkers argue that Democrats’ ambivalence about President Trump’s missile strikes against Assad have more to do with former President Barack Obama and his foreign policy legacy than the ghosts of the Bush presidency.

Obama famously warned the Syrian government that use of chemical weapons would cross a “red line,” forcing the United States to consider military action against Assad’s regime.

When the U.S. concluded in August 2013 that Assad had used chemical weapons against civilians in the Damascus suburb of Ghouta, Obama announced plans to launch missile strikes against Syrian military targets.

After the British Parliament rejected a bid for the United Kingdom to participate in the strike, Obama decided to seek congressional approval for the move. It soon became clear that the strike faced bipartisan opposition, and the White House pulled the request.

Despite public opposition to the retaliatory strike, Obama endured a lot of criticism, including from members of his own party, for not honoring his “red line” ultimatum, undermining U.S. credibility.

“The residue of the decision not to bomb in 2013 created an environment where the next time it happened a strike was going to be a foregone conclusion. There’d be no alternative,” said Steven Simon, who was senior director of Middle Eastern and North African affairs on Obama’s National Security Council in 2011 and 2012.

That leaves Democrats who want to avoid a replay of 2013 with limited grounds on which to criticize Trump, admitted Simon, now a history professor at Amherst College.

“They have sort of squared the circle by applauding the use of force but registering concerns about lack of congressional consultation,” Simon said.

Then there is the matter of deeper disagreement within the Democratic Party about Obama’s broader policy toward Syria. Obama rejected the suggestions of many advisers, including then-Secretary of State Hillary Clinton, to intervene more forcefully to protect Syrian civilians and speed up Assad’s ouster. Those disagreements were evident in Clinton’s campaign promise to create a no-fly zone in Syria, as well as her calls Thursday for the U.S. to take out all of Assad’s airfields ― a more ambitious step than Trump ended up taking.

Clinton and other proponents of greater intervention in Syria argue that by declining to diminish Assad, the U.S. will never have the leverage needed to stop his atrocities and forge a diplomatic solution.

As a candidate, Trump ran against Clinton’s strategy, repeatedly insisting that Assad was preferable to the Syrian groups trying to overthrow him.

For Democrats hoping Trump would adopt a more Clintonian approach, it is tempting to view his strike on the Syrian airfield as the beginning of a recognition that Assad must face greater pressure, including the threat of force, to end the conflict.

But one such proponent of more robust action, Michael Breen, president of the center-left Truman Center and Truman National Security Project, warned against getting too optimistic. Breen is concerned about Trump’s haste and apparent lack of strategy.

“A lot of people wanted to see the U.S. get more involved in Syria and wanted to see a response to the regime’s atrocities, but it is way too early to suddenly say Donald Trump is a different president than he was two days ago.”

Ryan Grim and Mike McAuliff contributed reporting.