Given that most new presidents round out their Cabinets with loyalists, it is a near certainty that the three Senators vying for the White House in 2008 would show a proclivity for filling their administrations with Members of the House and Senate.

But any inclination to do so faces a set of political realities that could make it difficult for a President-elect Hillary Rodham Clinton (D-N.Y.), Barack Obama (D-Ill.) or John McCain (R-Ariz.) to install a well-respected colleague in their Cabinet. That’s because any of the three would risk reducing their numbers in a narrowly divided Senate and in a highly partisan House, where they would need strength in numbers to pass an agenda of change in their first year at 1600 Pennsylvania Ave.

“The president is going to need every single vote he or she can get,” noted one Democratic strategist and former senior Senate aide. “It’s hard to make a case that it’s worth losing or putting at significant risk a Senate seat for a Cabinet-level position.”

McCain, Obama or Clinton would have to weigh the home-state politics of any prospective appointee. The Senators probably would be disinclined to name to their administration any House Member whose district could swing to the other party in a special election, or any Senator whose home-state governor — responsible for naming his or her successor — sits on the other side of the aisle.

“I’m not sure Speaker [Nancy] Pelosi [D-Calif.] or Sen. [Harry] Reid [D-Nev.] would look too favorably on attempts to poach members of their respective caucuses,” advised one Democratic Senate leadership aide.

Still, Democratic and Republican Senators alike predicted that McCain, Clinton and Obama would consider naming their fellow lawmakers — whom they know and trust — to one of the 15 Cabinet administration jobs ranging from State and Defense to Education and Veterans Affairs. As current Senators, McCain, Clinton and Obama share a level of familiarity with Congress that likely hasn’t been matched by a presidential hopeful since the last sitting Senator, John Kennedy (D-Mass.), won the presidency in 1960.

“It would be a logical assumption,” said Sen. Ben Nelson (D-Neb.), who was approached when President Bush was looking to name an Agriculture secretary in 2004. “Given that former governors go to their current or former governor colleagues for their cabinets, it would make sense for them to go to the groups that they know,” he said.

Certainly, like most of his predecessors, Bush relied heavily on his Texas allies when putting together a Cabinet in early 2001. And while he has some former House Members in his closest ranks — including Vice President Cheney and Office of Management and Budget Director Jim Nussle — none of Bush’s current secretaries moved directly to the executive branch from the House or Senate.

Yet, it isn’t unprecedented for presidents to pull from Congress. President Jimmy Carter tapped Sen. Edmund Muskie (D-Maine) to be his secretary of State at the end of his term, while President Bill Clinton tapped Rep. Les Aspin (D-Wis.) as his first Defense secretary and later replaced him with newly retired Sen. Bill Cohen (R-Maine). Former or retiring lawmakers often tend to be of greater appeal for presidents — escaping any political pitfalls.

“There are very talented people in the body with areas of expertise for which Cabinet members are needed,” said Sen. Johnny Isakson (R-Ga.), a McCain ally. “There’s a lot of talent in the Senate.”

The presidential appointment chase remains at least eight months away. Yet, names already are being floated as possibilities for Obama, Clinton or McCain, and they include at least a handful from the halls of Congress.

Atop McCain’s short list, according to closely aligned Republican Senators and aides, likely would be two of the Arizonan’s most vocal supporters: Sen. Lindsey Graham (R-S.C.) for attorney general or Sen. Joe Lieberman (ID-Conn.) as secretary of State, Defense or Homeland Security. Graham and Lieberman have been stumping for McCain for months and are considered two of the most loyal and ardent backers of his Iraq War policy.

“Those are two of the most obvious choices from the Senate,” observed one Republican Senate aide.

Other long-shot possibilities for McCain could include Senate Minority Whip Jon Kyl (R-Ariz.) at Treasury or Justice, Sen. Richard Burr (R-N.C.) at Veterans Affairs, or even conservative Sen. Sam Brownback (R-Kan.), who is retiring in 2010, as attorney general or secretary of Health and Human Services. Several GOP sources advised that a Brownback selection is unlikely, however, since Kansas is home to a Democratic governor and Obama supporter in Kathleen Sebelius.

In the House, Rep. Paul Ryan (R-Wis.) could be ripe for a post such as Treasury or head of the Office of Management and Budget. The latter position is not considered a Cabinet post but shares Cabinet status within the executive branch. Rep. Fred Upton (R-Mich.) could be considered to head the Commerce or Labor departments.

“Undoubtedly, [McCain] will look to his colleagues,” said Sen. Mel Martinez (R-Fla.), a McCain supporter who served as secretary of Housing and Urban Development during Bush’s first term. “He knows them well, and he trusts them. Out of 15, I wouldn’t be surprised if two or three would go to Senators.”

On the Democratic side, Clinton and Obama also are likely to at least look to their Congressional comfort zones when considering Cabinet posts. But Democratic Senators and aides cautioned that many majority-party Senators wouldn’t want to end their Senate career for a short-term Cabinet post, nor would either Obama or Clinton want to imperil passage of their agenda by dwindling the already narrow Democratic majority in the Senate.

Democrats are aiming to expand their majority of 51 to a filibuster-proof margin of 60 in the coming cycles.

The name most often mentioned for either Obama or Clinton is the one-time presidential contender and veteran Sen. Joseph Biden (D-Del.), who has remained neutral since exiting the race and who many say would be on the short list for either administration’s secretary of State. Biden comes from a Democratic state, and if he were offered and accepted the job, could leave his seat in safe in Democratic hands — possibly to make way for his son, Beau, who is Delaware’s attorney general.

The majority of the other Senators mentioned for various positions run up against the likely political disqualifier of sharing their state with a GOP governor, who almost certainly would tap a Republican to succeed them. For instance, Sen. Evan Bayh (D-Ind.), often named as a vice presidential prospect for Clinton, could be a possible secretary of Defense for the New York Senator, while Sen. Chris Dodd (D-Conn.) could be on the list as a possible State or Treasury secretary appointee under Obama. Democratic Sens. Jack Reed (R.I.) and Jim Webb (Va.) both have come up as possible secretaries of Defense for either candidate, but like Bayh and Dodd, Reed’s prospects are dim since the governor of Rhode Island is a Republican.

But the issue of gubernatorial politics matters little if the president-elect is looking for a token Republican. For instance, Sen. Chuck Hagel (Neb.), an anti-war Senator who is retiring, has regularly been mentioned as a possible Obama Cabinet selection.

Politically speaking, the House might be more fertile ground for Democratic administration picks, since the party now holds a majority of 231 seats to the GOP’s198. Yet House Members often are chosen for the less prominent jobs such as Labor, Housing and Urban Development, or Transportation.

Among the possible House Members are Rep. Jane Harman (D-Calif.) as secretary of Homeland Security under Clinton, or the possible Obama selections of Democratic Reps. Chet Edwards (Texas) at Veterans Affairs, Xavier Becerra (Calif.) at Labor or Housing and Urban Development, or Artur Davis (Ala.) at Justice. House Agriculture Chairman Collin Peterson (D-Minn.) could be a possible Agriculture secretary for either president-elect.

Clinton or Obama also could look to House Budget Chairman John Spratt (D-S.C.) for a job as the director of OMB.

But just like with the Senate, many of those lawmakers represent swing districts, which if left open, could be prime political ground for Republicans to advance their numbers. Edwards, Peterson and Spratt, in particular, represent seats that are viewed as potentially vulnerable if left vacant.

“Part of the choices will be determined on what the numbers are, and who they can get to replace them,” said Senate Associate Historian Don Ritchie.

Sen. Ken Salazar (D-Colo.) said, “there are a number of quality people in the House and Senate” who will certainly “be part of the pool” of prospective Cabinet picks. But Salazar, who insisted he wasn’t interested in leaving the Senate anytime soon, believes that the new president would put a premium on keeping their administration diverse — representing all different walks of life.

“I think you’ll see a combination,” Salazar said. “They are going to want to see the very best people run these important Cabinet positions.”