With the 2008 presidential nominees also doubling as Senators, their Democratic and Republican colleagues already are anticipating using the chamber as a key staging ground for the campaign and quietly plotting a months-long strategy to bring up politically divisive issues to force tough votes on the candidates.

Senators in both parties say it is inevitable that the Senate will serve as a sideshow for this year’s election since both parties will — for the first time in history — tap one of their own to serve as the presidential nominee. Sen. John McCain (Ariz.), a 22-year Senate veteran, has all but locked up the GOP nod for president, while Democrats are poised to field either Sen. Barack Obama (Ill.) or Sen. Hillary Rodham Clinton (N.Y.) as their party’s contender.

Certainly, no one expects the rivals to spend much time in the Senate in the coming months (They’ve been absent from the chamber for the better part of the 110th Congress).

But Senate Democrats are looking at holding votes related to the environment, health care or even the war that could force McCain to take politically toxic positions, miss key votes or reconcile previously held stands. Republican Senators also are hoping to do the same to the Democratic contenders, particularly on issues related to national security, taxes and spending, where they believe McCain has the upper hand against either Democratic rival.

“You can expect the debate to serve as a proxy or a stalking horse for the two parties’ positions,” assured one Senate Democratic leadership aide. “Neither [candidate] has shown a willingness to come back for votes, but that doesn’t mean we can’t use the amendment process to stir up trouble.”

Some of the strategy already is in play. Last month, for instance, Democrats accused McCain of flip-flopping his position on torture after the Arizona Republican voted against an intelligence authorizing measure they argued would have outlawed a practice known as waterboarding. Democrats tried to make the charge that McCain had changed his stand on the issue since he previously had voiced his opposition to waterboarding.

And that’s probably just the beginning. Democrats think they can put McCain at odds with his own party on issues such as stem-cell research, global warming and perhaps even immigration in the months ahead. They hope that on certain issues, they can force McCain to choose between aligning with conservatives or flexing his independent streak, both of which Democrats argue could be problematic for the GOP White House hopeful.

“For someone who was a maverick, and wore that as a badge of honor, there’s a lot of fertile ground there,” said a senior Senate Democratic aide. “He’s going to have to reconcile his new self with his old self.”

But Sen. Lindsey Graham (R-S.C.), McCain’s closest Senate ally, said Republicans aren’t going to simply let the Democratic majority work their will against his colleague. He argued that Republicans also will have ample opportunities this year to highlight the contrast between the two parties’ White House candidates.

“The majority will use their position to try to define the general election for president, and I think we’ll do some of that ourselves,” Graham acknowledged. “I think you can expect a lot of jockeying for advantage in the presidential field, from both sides.”

Republicans already have begun questioning Obama’s credentials on national security and foreign policy, and they believe they’ll have numerous chances in the Senate to force him — or Clinton — to show how they would serve as the commander in chief.

“I don’t see how the Democrats can structure a debate in the Senate on Iraq that is a huge win for them that doesn’t have a major benefit to McCain,” said one senior Senate Republican aide.

Republicans say they also will be looking for opportunities to paint the Democratic nominee as a “tax and spender,” especially when the two parties debate the fiscal 2009 budget, or later this year when the Senate takes on any appropriations bills. And like the Senate Democrats plan to do with McCain, Republicans also are likely to use the budget debate to force the Democratic nominee to defend his or her presidential proposals.

“There are lots of things that Obama has proposed out on the trail … there’s going to be opportunities for us to take those and introduce them as amendments, and Obama’s colleagues in the Senate are going to be put in a very tough position of having to vote against their nominee,” the senior GOP staffer said.

Sen. Judd Gregg (R-N.H.) put it this way: “Generally, what you are going to see are attempts from our side to push their side to the left, and amendments on their side to push our guy to the right. I think that’s where you will see it break down.”

Democrats, for their part, remember all too well how in the 2004 campaign, President Bush and the Republicans tried to use Sen. John Kerry’s (D-Mass.) Senate record against him. Still raw for Democrats is when Republicans accused Kerry of flip-flopping on the Iraq War since the Massachusetts Democrat supported its authorization in 2002 but later voted against a particular funding measure related to the conflict.

Sen. Byron Dorgan (D-N.D.) said it’s impossible to know how the next seven months will play out with two candidates also serving as sitting Senators, calling it “new territory for everybody.” But Dorgan acknowledged that Senators, in any campaign, “give support to the standard-bearers and help them brand their product.”

Sen. Frank Lautenberg (D-N.J.) reminded that “political inspiration” is attached to a lot of votes in the Senate, and there’s no doubt that will be the case as the 2008 campaign plays out. That’s inevitable, he argued, since the Senate is one of the few “free” forums for the candidates and is home to dozens of the contenders’ supporters and opponents.

“I’m sure this will be part of the theater of the presidential election,” Lautenberg said.

Still, Senators in both parties warned against entirely transforming the Senate into a political stage for the White House contest. Both McCain and the Democratic nominee need to attract independent and swing voters to their camp, a particularly important task in the face of an electorate disillusioned by partisanship.

“If either side is seen obstructionist or making it purely political, it could backfire,” said Sen. John Ensign (Nev.), chairman of the National Republican Senatorial Committee. “In this political environment, it certainly could.”