Denver ? A federal court has thrown out the last remaining challenge to Colorado’s congressional redistricting plan, saying the state Supreme Court resolved the case when it upheld a plan backed by Democrats.

Republicans said Thursday they expect to appeal to the U.S. Supreme Court. The ruling, handed down Wednesday and made available Thursday, is a setback for the GOP, which has been seeking to overturn the state’s congressional district map for two years.

States must redraw congressional districts every 10 years to reflect population shifts. Colorado’s redistricting after the 2000 census was handled by a state judge in 2002 because lawmakers were not able to agree on new boundaries.

Republicans took control of the state Legislature and decided in 2003 to draw new congressional districts.

After Democrats sued, the Colorado Supreme Court threw out the Republican map and restored the judge’s version. The court said redistricting can be done only once a decade, after the federal census but before the next general election.

The federal court suit was filed by a Democratic lawmaker and three Republicans. They contended the state Supreme Court had wrongly restricted the number of times the Legislature may redraw congressional districts.

House Speaker Andrew Romanoff, a Democrat, said lawmakers will try to develop a plan that would turn redistricting over to a commission, instead of having it done in the Legislature, where deadlocks are possible.

That would require voter approval because it would change the state Constitution.