Representative Ed Royce, Republican of California and the chairman of the House Foreign Affairs Committee, said his committee would hold a hearing in the coming days to examine American policy in the region. He said he expected the Trump administration to begin clarifying its views.
“Military force cannot be the only means of responding to these atrocities,” he said.
Democrats, who have found precious little ground on which to agree with Mr. Trump, generally offered narrower praise, with some denouncing the strikes — conducted alongside Britain and France but without Congress’s assent — as illegal.
Senator Chuck Schumer of New York, the Democratic leader, described “a pinpointed, limited action” as “appropriate” but warned the United States against being drawn into a larger war with the Syrian government.
Representative Eliot Engel of New York, the top Democrat on the House Foreign Affairs Committee, said he held little hope that the administration would succeed in deterring Syria from using chemical weapons.
“A year ago, when our military struck targets in Syria in response to another chemical weapons attack, I warned that such an action with no strategy to back it up would fail,” he said. “Tonight’s announcement seems like history repeating, and there’s no reason to expect a different result absent a broader Syria strategy.”
Senator Tim Kaine, Democrat of Virginia, who sits on both the Foreign Relations and Armed Services committees, said that Mr. Trump had seriously erred in not seeking Congress’s consent.
“President Trump’s decision to launch airstrikes against the Syrian government without Congress’s approval is illegal and — absent a broader strategy — it’s reckless,” he said.
Mr. Kaine warned that allowing Mr. Trump to strike a foreign power without such authorization could provide a dangerous precedent.
“Today, it’s a strike on Syria — what’s going to stop him from bombing Iran or North Korea next?” he said.
At the insistence of Mr. Kaine and others, the Senate Foreign Relations Committee is expected to begin debate this month on a new authorization of military force against terrorist and other extremist groups, including in Syria. The authorization, commonly referred to as an A.U.M.F., would replace a law passed shortly after the Sept. 11, 2001, terrorist attacks.
But it would not address Mr. Assad’s government or the possibility of a larger use of force to intervene in the Syrian civil war.
A handful of Republicans joined Democrats in questioning the validity of the operation. Representative Thomas Massie, a conservative Republican from Kentucky, quipped on Twitter that he could not recall the Constitution giving the president the authority to strike Syria.
In a statement, Senator James Lankford, Republican of Oklahoma, warned that “it is vitally important that the Trump administration honors the Constitution by working with Congress on further military action.”
“The United States is not at war with the people of Syria, and I anticipate that the administration will quickly present their long-term intentions to the American people,” he continued.
Still, not all Republicans had reservations. Senator Tom Cotton, Republican of Arkansas and one of Mr. Trump’s most vocal supporters in Congress, gave unqualified approval.
“The Butcher of Damascus learned two lessons tonight the hard way,” he said, referring to Mr. Assad. “Weapons of mass destruction won’t create a military advantage once the United States is done with you, and Russia cannot protect its clients from the United States.”
And Senator Lindsey Graham, Republican of South Carolina, urged the administration to act more aggressively, fretting, “I fear that when the dust settles this strike will be seen as a weak military response, and Assad will have paid a small price for using chemical weapons yet again.”
“Assad has likely calculated a limited American strike is just the cost of doing business,” he said. “Russia and Iran will view the limited action as the United States being content to drop a few bombs before heading for the exits.”