Republican Sen. Johnny Isakson still hasn't attracted a Democratic challenger. But he's drawn two other contenders hoping to derail his bid for a third term in the U.S. Senate.

Libertarian Allen Buckley said Wednesday he will run on the third-party ticket against Isakson next year. He joins Republican Derrick Grayson, a MARTA engineer and minister who garnered 1 percent of the vote in the 2014 Senate primary.

Isakson remains well-stocked for the challenge. The veteran Republican's campaign told us today that Isakson raised $1 million in the third quarter and now has about $5.4 million cash on hand.

Buckley, an attorney and accountant in metro Atlanta, ran as a Libertarian in the 2008 race between Republican Saxby Chambliss and Democrat Jim Martin, and his 128,000 or so votes helped force the race into a runoff that Chambliss eventually won. He also lost bids for the U.S. Senate in 2004 and lieutenant governor in 2006.

Buckley said this time around he thinks he can "possibly" win the election on a campaign of cutting the size of federal government and reining in programs.

“My campaign will emphasize the real issues and provide solutions to the significant problems our country faces, including excessive debt, entitlements, regulation and foreign intervention," Buckley said. "I do not believe any opponent I will face shall do the same."

Democrats are still searching for a challenger to run against Isakson after the Rev. Raphael Warnock said last week he has decided not to run for office. Warnock is the pastor Ebenezer Baptist Church, and party strategists hoped his bid would help energize minority voters.

Isakson, 70, raised more than $1 million in the third quarter, a continued decline from the numbers he posted in the first two quarters this year. Isakson recently announced he has Parkinson's disease, though he has said it would not jeopardize his ability to serve another six-year term.

And given his lack of Democratic opposition and the slew of more competitive Senate races nationally, it's been harder for Isakson to show donors he needs the cash.

Still, Isakson campaign consultant Heath Garrett said Isakson's haul this year and cash on hand levels are records for Georgia U.S. Senate candidates in an off-year.