Beyond complaints about a lack of consultation, 116 House representatives (98 Republicans, 18 Democrats) signed a letter demanding a vote in Congress before any assault is launched against Syria. Fifty-four House Democrats (some of whom signed that first letter) wrote Obama on Thursday asking him to "seek an affirmative decision of Congress prior to committing any U.S. military engagement" in Syria.
Libertarians like Sen. Rand Paul, R-Ky., have also suggested that Obama lacks the power to order an attack against Syria, and moreover, Paul argued that Syria has "no national security connection to the United States."
All the while, the administration emphasized that Obama had not made any decision about how or whether to proceed with an attack.
"The president hasn't made a decision yet," Vice President Joe Biden said at a morning event about guns at the White House. (Engel said after Thursday's briefing that the administration still hadn't made any decision.)
But while the administration had telegraphed its desire to proceed with targeted strikes as early as Thursday, that process has been slowed by internal political debates in the countries that had seemed poised to join an international coalition.
Polls suggest the public has little appetite for U.S. involvement in Syria's protracted civil war. NBC News' poll released Friday found that nearly 80 percent of Americans believe Obama should receive congressional approval before using force, and 50 percent believe the United States should not intervene.
But Congress' demand for more consultation from Obama threatens to delay the process further, thereby risking a slow bleed of public support from any attack. If lawmakers demand to first vote on intervention, it could delay matters further. Congress is set to return from its break on Sept. 9.
Coloring the whole debate is a public hangover from two extended wars in Iraq and Afghanistan last decade. Iraq, where American involvement was seen as elective and based on intelligence that turned out to be false, has particularly set the context for the debate about Syria. British lawmakers repeatedly invoked Iraq during their debate on Thursday.
A State Department spokeswoman rejected the comparison on Thursday.
"Iraq and Syria are in no way analogous, we are not considering analogous responses in any way," spokeswoman Marie Harf said.
—By Michael O'Brien, Frank Thorp and Stacey Klein, NBC News. Catherine Chomiak and Carrie Dann contributed reporting.