So what would happen if the congress votes "no", and then Obama decides to attack anyway? What would happen if the Pentagon said "Sorry, the people said no, we aren't going there"? Can that happen, what are the odds it would?
Barry can still attack even if congress says "no", Pentagon has nothing to do with it, they follow orders. But Barry won't without approval of Congress, he is looking for a way out and if Congress says "no" he will blame them....he blames everyone for everything cause he never had a father at home to beat his spoiled az.
To expand on this.
Only congress has the power/authoirty to declare war on another country/government.
Should congress say no, the president now has more limited options. Like prior presidents before him he can still order the military to attack for up to 90 days under his authority. Not sure what it's called but other presidents have done this before.
if congress does not like this they always have the legal option to start an impeachment process to remove a sitting president.
That I know of this has never occured in our history (impeachment due to president going to war without congrees's approval)
As for your question of the pentagon saying no.
The pentagon (ie. armed forces) just follow orders. If the pentagon were to say no (which again it has never done so in our history that I know of) then we have much bigger issues than Syria. We have something close to a miliatry coup on our hand. You have more of a chance of winning POWER BALL then seeing that occur.
What DragonGunner said is correct. By the president going to congress he has pertyy much but the ball in their court and politically they can take the blame. Granted with the world not wanting to get involved in the matter their might not be much blame to get for not doing anything.