With the next president coming to the Oval Office straight from the Senate, Cabinet appointees next year could have a distinctly senatorial flavor. And that means congressional vacancies.

In fact, if John McCain or Barack Obama appoints even two or three senators to the executive branch, the vacancies in the upper chamber could shift the balance of the next and future Congresses by multiple seats, as many potential appointees come from states where they would be replaced by governors of the opposite party.

Over the same span, though, only one man has been elected president straight from the Senate — John F. Kennedy. McCain and Obama have both spent enough time in the chamber to build relationships with several colleagues they could tap in a new administration.

Experts say that makes it somewhat more likely that a few senators could vacate their seats for a role in the executive branch — particularly with McCain, whose 22 years in the Senate are a decade more than any president in history.

Jennifer Duffy, a Senate race analyst with The Cook Political Report, said the confluence of circumstances could add to the waning number of senators-turned-secretaries.

“I think maybe you’ll see a couple [senators], and there may be people who want to leave,” Duffy said, suggesting that members like Sen. Chris Dodd (D-Conn.) might be looking for a new challenge after decades in the Senate.

Dodd’s Connecticut colleague is perhaps the most likely Cabinet pick at this point, with many seeing Sen. Joe Lieberman (I) as a near shoo-in for Defense secretary under McCain.

If either Dodd or Lieberman is picked, Republican Gov. Jodi Rell would appoint a replacement, which would effectively flip the seat, since Lieberman currently caucuses with Democrats.

Altogether, among those considered potential Cabinet members, Lieberman’s and Dodd’s selections would be two of many that could flip a seat into the opposition party’s column.

Sen. Sam Brownback (R-Kan.), for instance, is retiring from the Senate in 2010 and is seen as a potential attorney general.

But appointing him would cause him to vacate the seat early and give Democratic Gov. Kathleen Sebelius the chance to appoint a Democrat who could build up incumbency before an election in 2010, at which time a full term would be at stake.

Similarly, the appointment of either Sen. Arlen Specter (R-Pa.) or Sen. Olympia Snowe (R-Maine) would allow Democratic governors to appoint replacements.

Specter is seen as a possible Veterans Affairs secretary, along with Sen. Richard Burr (R-N.C.). Burr’s state is currently led by a Democrat, but a tight race this year will decide the new governor, meaning that race would likely determine which party grabs the seat.

The result would also be up in the air if Sen. John Thune (R-S.D.) is appointed. Republican Gov. Mike Rounds would be able to appoint a temporary replacement, but a special election would follow just three months after the vacancy.