"I believe U.S. military action of the type contemplated here might prove to be counterproductive," Rubio said. "After a few days of missile strikes, it will allow Assad, for example, to emerge and claim that he took on the United States and survived."
Paul, a Kentucky conservative with strong tea party ties, has threatened a filibuster, although he acknowledged that proponents have the votes to prevail in the Senate, and he pinned his hopes on the House.
The notion of a contained operation has failed to sway many Republicans and Democrats in the House, who question why the U.S. should get involved now in a Syrian civil war that has killed an estimated 100,000, displaced millions and is in its third year. While House Speaker John Boehner, R-Ohio, and Majority Leader Eric Cantor, R-Va., have expressed support for military action, but rank-and-file Republicans remain reluctant or outright opposed.
Republican Rep. Chris Collins said voters in his western New York district are "overwhelmingly against involvement." The freshman congressman is undecided.
"Really, I'm looking for the president to justify limited military strike and establish what are the objectives he's seeking and what is the mission," Collins said in a phone interview.
Kerry told the Foreign Affairs Committee that he believed Obama would address the nation on Syria in the next few days. The president returns home from overseas Friday night.
Speaking in Sweden on Wednesday, Obama left open the possibility he would order retaliation for the deadly chemical weapons attack even if Congress withheld its approval.
"I always preserve the right and responsibility to act on behalf of America's national security," he told a news conference. In a challenge to lawmakers back home, he said Congress' credibility was on the line, not his own, despite saying a year ago that the use of chemical weapons would cross a "red line."