It’s been nearly 50 years since a sitting Senator was elected president, but perhaps even more remarkable is the possibility that voters could tap a pair of current Senators to square off for the job in November — an unprecedented occurrence that would make 2008 an even more extraordinary election year.

The dynamic — while far from assured — also heightens the opportunities for the remaining Senators, who have spent seven years struggling for access, influence and negotiating power against a sometimes adversarial executive branch. Indeed, regardless of whether Democratic Sens. Hillary Rodham Clinton (N.Y.) or Barack Obama (Ill.) or Republican Sen. John McCain (Ariz.) wins the presidency this November, Senators in both parties believe they may have a historic opportunity to ease the often tense relationship between Capitol Hill and 1600 Pennsylvania Ave.

“There would be a greater respect for the legitimate roles the two branches play that’s been lacking for a long time because for a long time we’ve only elected governors to the White House,” said moderate Sen. Gordon Smith (R-Ore.), who is backing McCain. “There are practical difficulties to being elected [president as a Senator], but there’s a practical benefit once elected.”

“Someone who understands and has served in Congress certainly would have an advantage in the White House,” agreed Sen. Byron Dorgan (N.D.), who is uncommitted in the Democratic primary race. “They would understand how to get things done and what needs to be done.”

By any measure, Congress’ relationship with President Bush, a former Texas governor, has had its ups and downs. Republican and Democratic lawmakers alike have complained about the Bush administration’s often-isolated approach to governance and its attempts to expand executive powers, especially on issues related to terrorism and national security. Only recently, many Senators say, has Bush sought to bring lawmakers more into the fold — a move that some say was by design and others say was by circumstance after Democrats won control of the House and Senate in 2006.

“We’ve had some presidents who’ve lacked an understanding of how Capitol Hill works,” acknowledged Senate Majority Whip Dick Durbin (D-Ill.). “It’s a long learning process.”

A senior Democratic aide said that in recent months Bush has seemed more interested in negotiating deals and communicating with Congress, and at least given more face time to House and Senate leaders. This aide said it would seem likely that a Senator as president would put an even greater premium on that outreach, but then again, it is impossible to predict how any administration will deal with lawmakers.

“Theoretically, having a former Member elected directly to the presidency would set up a better situation than what we have now — but that’s all theory,” the aide said. “There’s been very little respect for Congress as a coequal branch of government.”

Senate Minority Whip Jon Kyl (R-Ariz.) defended the Bush administration’s record of dealing with Congress, arguing that the president made numerous attempts to make inroads with lawmakers, even on politically caustic issues such as Social Security and immigration reform. Kyl, however, did concede that it would seem likely a Senator in the White House would have “a potential upside to it” in terms of using that experience to turn ideas into law.

“Theoretically, they have a greater knowledge of how things are done or not done,” Kyl said.

In all, just two sitting Senators have ascended directly into the presidency: Sens. Warren Harding (R-Ohio) in 1920 and John F. Kennedy (D-Mass.) in 1960. Never in the nation’s history, however, have two current Senators secured their parties’ nominations at the same time and dueled in a general election contest.

Yet the prospect is quite real this year as two Democratic frontrunners, Clinton and Obama, battle for their party’s nomination, while McCain looks to hold onto his momentum and secure the nod in the GOP primary contest. As of Tuesday, the chances were good that two of those three Senators would be atop the ballot for president in November.

Sen. Ben Nelson (D-Neb.), an Obama supporter with a penchant for compromise, said he’s confident that, if elected, any one of his three Senate colleagues would improve the relationship between the legislative and executive branches. Nelson argued that a Senator turned president would not only have a unique understanding of how Congress operates, but also would come armed with long-standing House and Senate friendships.

“You’d have a line in” to the Congress, Nelson said. “It’s not only that personal working relationship with one another, but it’s that common understanding. They wouldn’t lose interest in what’s happening in Congress. They are going to be more focused on what’s happening in Congress. It’s just natural.”

“The better you know people, the better the communication — that’s a given,” echoed Sen. Johnny Isakson (R-Ga.).

To be sure, Bush isn’t the only president in recent years to do battle with Congress. Former President Bill Clinton, also a one-time governor, had more than his share of Congressional critics as well, even from within his own ranks, for failing to communicate openly and take time to learn about the complexities of the legislative branch.

A Senate Republican leadership aide said Senators have “a much better understanding of the currents of the Senate that you can’t get anywhere else.” This source added that a Senator would have firsthand knowledge of how difficult it can be to move legislation through a divided Congress and, more importantly, an insider’s guide to “which Member to call to move what issue.”

“It’s sort of like having a quarterback who has only watched football and then gone out to play, or having a quarterback who has won a Super Bowl,” the Republican aide suggested.

And while Democratic and Republican Senators appear to universally agree that one of their own would show a greater respect for the legislative arm of government, few lawmakers believe the days of partisan clashes between the president and Congress would be over.

“It doesn’t mean there wouldn’t be very big pitch battles,” Dorgan said.

For instance, if McCain were elected president, Democrats in Congress would still have “partisan divisions and ideological differences” with the Arizona Republican, noted Sen. Bob Menendez (D-N.J.). But Menendez, who is backing Clinton in 2008, said any of the three Senate presidential frontrunners would have “an understanding of the give and take and an understanding of the negotiations” that are at the heart of advancing any legislative agenda through Congress.

The prospect of a President Clinton, Obama or McCain, Menendez said, “bodes well for the relationship with the Senate in terms of moving an agenda for the country. A Senator who understands the ways of the institution and has good relationships can go a long way.”