The presidential election season has officially hit Capitol Hill.

While six members of the Senate and four House lawmakers launched presidential bids early last year, 2008 politics didn’t significantly affect the congressional agenda until this month.

Republicans last week circled their wagons around Sen. John McCain (R-Ariz.) as they moved to avoid a showdown with Democrats on an intelligence bill dealing with torture. When they punted a controversial bill on waterboarding to the White House, Senate Republicans gave political cover to McCain.

McCain has been outspoken against waterboarding, but did not agree with the bill’s language that would have set up a uniform set of policies that apply equally to spy agencies.

Similarly, Senate Republicans reversed course on an Iraq withdrawal measure Tuesday. Instead of rejecting cloture on Sen. Russ Feingold’s (D-Wis.) bill, they reversed strategy and voted for it. The procedural motion attracted a surprising 70 votes, with more Republicans than Democrats backing it.

Republicans are expected to vote against Feingold’s bill when it comes to a vote, but their shift in strategy is a clear indication that they want to debate Iraq, as does McCain. GOP lawmakers believe the tide has shifted on the war and that the situation will continue to improve there, which would help their electoral prospects in November.

Many anti-Iraq war legislators, meanwhile, are also pleased to engage in that debate.

The Republican game plan comes with serious political risks. If the situation in Iraq worsens — something that is mostly beyond their control — McCain and the GOP minority in Congress will be crushed this fall. Yet Republicans know that most voters see the war as a Republican-led initiative. Most Senate Democrats voted for it in 2002, while a majority of House Democrats rejected it. Regardless, Republicans cannot avoid the topic and have decided to take the offensive.

Congressional oversight is also being driven by presidential politics.

During a House Small Business Committee hearing on Tuesday, Minnesota Gov. Tim Pawlenty (R) debated Democrats on how to address the nation’s healthcare woes. But a lot of the chatter surrounding the hearing had nothing to do with healthcare and everything to do with the 2008 ticket, because Pawlenty is a possible vice presidential candidate.

Across the Capitol on Tuesday, Army Chief of Staff Gen. George Casey got caught in some presidential sparring during a Senate hearing. Members sought answers to Sen. Barack Obama’s (D-Ill.) recent claim that an Army captain had told him he had to lead a platoon in Afghanistan that was short on men, ammunition and Humvees.

After Sen. Lindsey Graham (R-S.C.), a longtime McCain ally, pressed Casey on Obama’s assertion, Sen. Claire McCaskill (D-Mo.) said, “Well, since we had a McCain moment, I think we need to have an Obama moment out of fairness.” She then proceeded to ask her question.

White House fever has hit the Capitol, and it will only intensify during the next eight months.