No one expects Georgia Sen. Johnny Isakson to lose in November. The two-term Republican may just need to campaign for a few more months to hold onto his seat. 

Winning in the Peach State requires carrying more than 50 percent of the vote. And Republicans aren’t sure he’s going to get there next month. 

“It’s likely Georgia will go to a runoff,” said a GOP Senate campaign aide. 

The competitiveness of the presidential race in this traditionally red state, combined with the fact that Isakson is running in a three-way race, makes winning a majority on Election Day harder for him.

If he doesn’t, he and the likely second-place finisher, Democrat Jim Barksdale, will square off in a Jan. 10 runoff.

A special election at the beginning of next year’s legislative session is a cost Isakson would prefer to avoid. The campaign would have to spend big to get voters to tune in and show up in the midst of the holiday season and college football playoffs. 

Still, he’s expected to win if it comes to that.

It’s what happens between now and November that’s more unpredictable. 

Isakson leads Barksdale by more than 16 points in the latest RealClearPolitics average, carrying between 41 and 55 percent of the vote in the four most recent public polls.

“They’ve done a good job dealing with what they can control,” said Chip Lake, a Republican consultant in Georgia, about the Isakson campaign. “It’s what they can’t control that’s what I would suspect has them concerned.”

And what’s uncontrollable?

Donald Trump.

“Donald Trump is hemorrhaging white women very quickly across the country, and Georgia is not immune to that,” Lake said at the end of last week — before revelations of a 2005 recording in which Trump bragged about groping women. 

Like most red-state Republicans running for Senate this year, Isakson condemned Trump’s remarks but has stood by him as the nominee. 

Trump has held a single-digit lead in Georgia this fall, but internal polling shows the state could be in play for Hillary Clinton, who bulked up her staff there in August. 

[Democrats Think Georgia Is Starting to Trend Their Way]

Even if Republicans turned off by Trump don’t cross over to vote for Barksdale down ballot, they may not show up to vote at all, hurting Isakson. 

“Reaching the 50 percent plus 1 required for outright victory in Georgia has always required an Isakson coalition of Republicans, Libertarians, independents and Reagan Democrats,” Isakson campaign manager Trey Kilpatrick said in a statement.

Prominent Georgia Democrats have donated to the senator’s campaign. And Rep. David Scott summed it up this way: “I’ve always voted for Johnny Isakson. He’s my friend. He’s my partner.”

The elephant in the room in any discussion about Isakson is his Parkinson’s diagnosis, which he revealed last year. But if anything, Lake said, Isakson is campaigning even harder than usual.

“They are not going to get caught sleeping,” said Lake, who still expects that Isakson can over-perform Trump enough to win on Nov. 8.

The bigger challenge, Lake said, is to keep donors and grass-roots activists from writing off the race as an effortless victory.