Markey, who was elected to the seat that Kerry vacated when he joined the Cabinet, said the legislation under consideration was too broad, "the effects of a strike are too unpredictable, and ... I believe we must give diplomatic measures that could avoid military action a chance to work."
Said Mulvaney: "While I am concerned about taking no action, it strikes me that international law cannot be upheld via unilateral attack by the United States."
Yet Maryland Rep. Steny Hoyer, the second-ranking Democrat in the House, said, "It would be inimical to our country's standing if we do not show a willingness to act in the face of the use of chemical weapons and to act in a limited way to address that use alone."
Hours before Obama's speech from the White House's East Room, Hoyer added, " I don't think there's any doubt that failure to do so would weaken our country, create a more dangerous international environment and to some degree undermine the president of the United States."
Earlier, Senate Republican leader Mitch McConnell became the first congressional leader to come out against legislation giving the president authority for limited strikes. "There are just too many unanswered questions about our long-term strategy in Syria," he said.
By contrast, Speaker John Boehner of Ohio and Majority Leader Eric Cantor of Virginia, the top two Republicans in the House, have endorsed Obama's request.
Given the uncertainty of diplomatic maneuvering, no vote is expected for several days, if then.
"If something can be done diplomatically, I'm totally satisfied. ... I'm not a shock and awe guy," said Senate Majority Leader Harry Reid in a reference to the massive display of firepower that opened the war in Iraq nearly a decade ago.
Still, there was ample skepticism in Congress about the United Nations as well as Russia's true intentions, as well as Syria's willingness to be bound by international agreements.