Western diplomats insisted that the threat of strikes was a critical ingredient that would ensure Syrian compliance. But Russian officials said that a diplomatic route would work only if the United States and its allies renounced the use of force.
And experts questioned whether it would be possible to transfer stockpiles of chemical weapons to an international monitor amid a civil war that has killed more than 100,000 people.
Still, Obama said Tuesday night that he wants to give the process more time, and he dispatched Kerry to meetings in Europe to work out the details of a potential U.N. agreement.
The president said he turned to Congress for authorization because he thinks that any action would be stronger if backed by lawmakers, especially after more than a decade of war.
Obama’s speech did not immediately appear to change minds on Capitol Hill. A number of Democratic senators expressed support afterward for his diplomatic approach, while remaining wary of military action. Most Senate Republicans who were on the fence remained unconvinced.
“I don’t think the case for military action has been made,” said Sen. Charles E. Grassley (R-Iowa). But, he added, “the Russian proposal to force Assad to turn over chemical weapons to international monitors presents a possible alternative.”
Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.) said they regret that Obama “did not speak more forcefully” about providing military assistance to moderate opposition groups in Syria and for not laying out “a clearer plan to test the seriousness” of the Russian proposal.
House Minority Leader Nancy Pelosi (D-Calif.) argued that the administration’s threat of force has already yielded benefits.
“The president using the credible threat of American military action to bring diplomatic solutions back to the table demonstrates the strength of his leadership and his willingness to exhaust every remedy before the use of force,” she said.
Obama had previously taken his argument to Capitol Hill to lobby lawmakers, saying that he would pursue the diplomatic option but that the United States must be prepared to strike if it failed.
Lawmakers emerging from the meetings agreed that the diplomatic route should be given a chance.
House Speaker John A. Boehner (R-Ohio), one of the few members of either party in the House who backs a military strike, said he suspects the new proposal is a stalling tactic.