Republican leaders in Congress, faced with an increasingly restive rank and file, are warning that they will demand a change of course in Iraq unless they see clear evidence of progress by October.

Even as they back President Bush in his battle with Democrats over the final wording of a war funding bill (HR 1591) that the president vetoed May 1, GOP leaders acknowledge that their support for a continued U.S. military effort in Iraq is not open-ended.

House Minority Leader John A. Boehner, R-Ohio, interviewed on Fox News Sunday, insisted it is still too soon to tell whether Bush’s deployment of more troops to Iraq is achieving its objectives. Boehner said there were signs of “some success on a number of fronts.” But he added, “By the time we get to September, October, members are going to want to know how well this is working, and if it isn’t, what’s Plan B.”

But first, Republican and Democratic leaders on Capitol Hill must find a way out of their standoff and get a revised spending bill to Bush before the military runs out of needed operational funding.

One option: political benchmarks for the Iraqi government. While a failure to meet the benchmarks would not trigger a U.S. troop withdrawal as proposed in the vetoed bill, it could lead to a cutoff of non-military aid under one formulation being discussed.