Pelosi has no say over what goes on in Iraq or anyplace else. George W. Bush is our commander-in-chief.
and Pelosi holds the purse strings. Congress can designate what things it will fund (bringing home troops from Iraq, for example) and which things it will not fund at all (transporting soldiers to Iraq, for example) and that's that.
Not to mention that a lot of Republican Senators are up for election next time around. Those who know which side their bread is buttered on are putting as much distance between themselves and Bush's policies as possible.
