"If I run again, I will run a strong campaign, is what I meant. But only if I run again, and it's far too soon to make that statement," he said, according to The Associated Press.

Johnson is one of nearly half a dozen Democrats watched warily by the party for the prospect that he'll retire.

After suffering bleeding in his brain, the senator had surgery in 2006, and though he insists he's in good health, the condition has affected his speech and facility with movement.

But he insisted to reporters that his health would have nothing to do with his final decision on running again.

"I'm good to go. I feel great," Johnson said.

Democrats face an uphill battle to begin with for the upcoming cycle, as they'll have to defend 20 seats, a number of which — including Johnson — are in states Mitt Romney won this year. They have narrow opportunities to play offense in the 13 seats held by Republicans, most of which are safe seats for the GOP.

But that narrative is similar to the one Democrats faced two years before, and they managed to defend every incumbent and expand their majority by two. The party is insisting it can pull off a similar feat this cycle.

This story was updated at 9:28 a.m.