Among those in the middle from either side, the main questions are whether the limited strikes Obama proposes will work, and if unintended consequences will lead to U.S. involvement in another war halfway around the world after more than a decade of fighting in Iraq and Afghanistan.
"We don't know what's going to happen the day after we bomb," Democratic Rep. Bill Pascrell of New Jersey said Thursday on CNN.
The Senate version of the resolution approved by the Foreign Relations Committee sets a 60-day deadline for use of force in Syria, with an option for an additional 30 days.
An amendment accepted by the panel from Republican Sen. John McCain of Arizona and Democratic Sen. Christopher Coons of Delaware added language to say the military response was intended to reverse Assad's battlefield momentum, a stronger objective than had been outlined by administration officials.
The resolution also makes clear there would be no U.S. boots on the ground as part of a response in Syria. It now goes to the full Senate for an expected vote next week, when the House also will take up the issue.
A concern for House members and senators facing re-election next year is a primary challenge by a more extreme candidate who could attack them for backing the president's proposed military move.
Already, Senate Republican leader Mitch McConnell of Kentucky and veteran GOP Sen. Mike Enzi of Wyoming face primary races against opponents claiming stronger conservative credentials. Both McConnell and Enzi are undecided on a military response in Syria.
With polls showing public opposition to a military attack on Syria, legislators are facing pressure at home. Democratic Sen. Dianne Feinstein of California, who chairs the Senate Intelligence Committee, acknowledged Thursday that her constituents don't like the resolution.
"Every day I get a report on what the calls are, where the calls are coming from, what the nature of the argument is and there is no question that what is coming in is overwhelmingly negative," said Feinstein, who then added that "they don't know what I know, they haven't heard what I've heard."
A supporter of a military response in Syria who won re-election last year, Feinstein I like to believe now after 20 years I have some skill in separating the wheat from the chaff in this thing."
However, GOP Rep. Matt Salmon of Arizona said he remained unconvinced.
"I agree that there are sometimes that you need to just go out and lead and do what you believe is the right thing to do and hope that you can convince the people to follow," Salmon told CNN. "But, right now, I don't think that this administration has provided a very, very winning argument or series of arguments that we should engage in this conflict."