U.S. Sen. Johnny Isakson plans to formally announce next week that he’s running for re-election, putting to rest rumors that he won’t seek a third term in the upper chamber.

Georgia’s soon-to-be senior senator, who has said for weeks that he is readying another campaign, plans to outline his plans Monday at a statehouse event. The Cobb County Republican’s aides expect Gov. Nathan Deal, Lt. Gov. Casey Cagle and state House Speaker David Ralston to be on hand in a show of GOP unity.

The backdrop is more than symbolic. The stiffest challenge for Isakson, who will turn 70 next month, could well come from within his own party in 2016. The advent of the tea party movement and the prospect of a bitter primary fight were among the factors that led his longtime GOP colleague, U.S. Sen. Saxby Chambliss, to decide against standing for re-election this month.

Isakson's political future has been the topic of rampant speculation in some Republican circles. U.S. Reps. Tom Price and Tom Graves are among House Republicans said to be keeping tabs on the job, along with outsiders including businesswoman Kelly Loeffler. Former U.S. Rep. Allen West of Florida is also often mentioned as a potential challenger, though he has dismissed such talk.

Isakson remains a favorite among establishment Republicans, and he recently fired up crowds stumping for Deal and David Perdue, who will fill Chambliss’ seat following his election victory last week. But Isakson’s consensus-minded approach on some testy issues has irked tea party groups and other conservative outfits itching to challenge him.

One measure of their frustration: A tea-party backed group last year ran a series of ads slamming Isakson for voting on a bill to continue funding the federal government, calling it a tacit endorsement of the Affordable Care Act. The Republican voted against the health care measure in 2011.

Several rising Democratic contenders are also closely watching the race, though it’s unclear whether a marquee candidate would risk challenging Isakson after Michelle Nunn’s eight-point loss last week to Perdue. Isakson handily defeated Democratic challengers in 2004 and 2010.

Isakson said in an interview that he has hired key campaign staff and is prepared for the long road ahead. He already has at least $2.2 million in the bank, and his aides said he's lining up fundraising events to add to his campaign fund.

“Georgia’s been good to me,” Isakson said. “And I’ve tried to be good to Georgia.”