Even as Congress considers President Obama's push for military strikes on Syria, the details of that plan continue to change by the day -- with one source telling Fox News that military officials have been asked to revise their plans 50 times since the Pentagon first began considering a “limited” action.

Still to be resolved is what method of attack the U.S. would use. While missile-equipped ships are at the ready in the Mediterranean Sea, a senior defense official told Fox News that the possibility of launching military aircraft strikes was one of the range of options presented to Obama.

The official said the choice the president makes will depend on what he wants included in the target list – and that seems to shift daily.

The regularly fluctuating plans could feed into congressional uncertainty as members prepare to consider a draft resolution next week authorizing military action there.

Polls show that any military strike, even a limited one, remains deeply unpopular – putting extra pressure on the president when he returns from a visit to Russia, where he’s attending a G-20 summit meeting.

Constituents also have been putting pressure on their congressional representatives to oppose a strike.

“I have spoken to hundreds of constituents,” said Rep. Jeff Duncan, R.-S.C, during a House committee hearing Wednesday. “No one… in my district in South Carolina or the emails of people that have contacted my office say ‘go to Syria and fight this regime.’”

Sen. Joe Manchin, D-W.Va., a one-time supporter of limited action, backed off Thursday saying, “given the case that has been presented to me, I believe the military strike against Syria at this time is the wrong course of action. I cannot support the Senate Foreign Relations Committee resolution and will be working with my colleagues and the administration to develop other options.”

Secretary of State John Kerry and other top administration officials who testified on Capitol Hill this week argued military action would not mean getting involved in a war but rather it would be “limited” in scope to punish the regime of Syrian President Bashar Assad for using chemical weapons on civilians.