With Sen. John McCain (Ariz.) now positioned to secure the Republican presidential nomination, attention in Arizona will shift to Gov. Janet Napolitano (D) and whom she might appoint to replace him in the Senate if he winds up winning the White House.

Arizona law requires that the appointee be from the same political party as the outgoing Senator, meaning Napolitano — a Democrat with designs on higher office herself — must appoint a Republican to replace McCain if he is elected president. That individual would serve until the next regularly scheduled general election in November 2010, when McCain’s current terms expires.

Napolitano’s office declined to comment on Wednesday, but the Arizona Democratic Party said the governor would act in the best interests of her state when appointing a replacement for McCain, should she be faced with that task.

“Gov. Napolitano will do whatever is best for the state, just like she’s always done,” state Democratic Party spokeswoman Emily Bittner said.

The 2008 presidential race is likely to boil down to a contest of sitting Senators, as the battle for the Democratic nomination has narrowed to a fight between Sens. Hillary Rodham Clinton (N.Y.) and Barack Obama (Ill.). But the Democratic governors of Illinois and New York would have the easy task of appointing a fellow Democrat to replace a Senator from their own political party.

Napolitano, a high-profile Democrat who endorsed Obama for president and is believed to have designs on running for Senate, serving in a presidential cabinet or both, would have to appoint a Republican to replace McCain, navigating state, national and personal political concerns in the process.

Republicans have said repeatedly that Napolitano will do whatever is politically expedient — and it is entirely possible that Napolitano would select a Republican with the understanding that that individual would agree to serve only the remainder of McCain’s term and not run for a full six-year term in 2010.

Democrats familiar with the governor say she is likely to choose from a bevy of her Republican supporters or gubernatorial cabinet members who are Republicans in the event that McCain assumes the presidency.

Among her high-profile GOP supporters are former Arizona Attorney General Grant Woods and Jack Jewett, a Tucson businessman and longtime member of the state Board of Regents. Republican elected officials who backed Napolitano in her 2006 re-election bid include Flagstaff Mayor Joe Donaldson and Phoenix City Councilman Tom Simplot.

If Napolitano turned to a member of her cabinet to replace McCain, she’d have several choices, including Bill Bell, director of the state Administration Department; Susan Gerard, director of the state Health Services Department; Don Butler, director of the state Agriculture Department; and Gale Garriott, director of the state Revenue Department.

Arizona Democrats say Napolitano has first dibs on the 2010 Senate nomination, should she choose to run. If she opts against running, Democrats could turn to Democratic Reps. Gabrielle Giffords or Raúl Grijalva, or state Attorney General Terry Goddard (D).

Wealthy businessman Jim Pederson (D), who lost to Sen. Jon Kyl (R-Ariz.) in 2006, also could be viewed as a viable candidate.

If McCain has relocated to 1600 Pennsylvania Ave. NW — or loses the presidency but chooses not to run for re-election — Republicans have several potential candidates for 2010, including Reps. Trent Franks and John Shadegg.

“We get a lot of Republicans who tell us they’d like to see Congressman Trent Franks or John Shadegg succeed [McCain] in the Senate,” Arizona Republican Party spokesman Sean McCaffrey said. “It seems a bit early to speak to either of them about this, but based on their record in the House, either would make a great U.S. Senator.”