Former U.S. Sen. Max Cleland blasted a Republican group that ran an ad invoking the image of Osama bin Laden, calling it a "smear" tactic from conservatives struggling to hobble Democrat Jon Ossoff's special election campaign.

He was referring to a digital ad launched by the Congressional Leadership Fund that showed the image of the slain jihadist while panning Ossoff's documentary work with the Al-Jazeera TV network. And Cleland knows of which he speaks: In the 2002 race for the U.S. Senate, Republican Saxby Chambliss employed an image of bin Laden in an attack on the incumbent Democrat.

"This is what Republicans do if they don't have a real case or a real candidate," said Cleland. "They try to smear the Democrats. They're lying. And the public can see through that."

The ad calls Al Jazeera a "mouthpiece for terrorists," citing a a 2011 piece on the rising news organization in the American Journalism Review that also called the Qatari-owned network a legitimate and influential source of Middle East information despite some questionable editorial decisions. Other critics have panned what they have called a cozy relationship The New York Times Magazine .

Ossoff has come under fire from conservative groups for his work with the network, which has become fodder at GOP meetings across the district. His campaign said he's proud of his time "working for outlets all over the world" including the BBC and Al Jazeera.

Ossoff is the surprising frontrunner in the April 18 special election for the 6th District, a conservative-leaning swath that spans from east Cobb to north DeKalb. The seat has long been a Republican stronghold, and Ossoff hopes to turn the race into an early test of the president's popularity with a vow to "stand up to Donald Trump."

Cleland said he expects the attacks to escalate as Ossoff aims to win this month's election outright to avoid a June 20 runoff.

"Republicans fear this becoming the national news. They fear it like the plague," said Cleland. "They know this would put fear in the soul of every Republican running for office."

More AJC coverage of the Sixth District race:

Ossoff pulls in record donations for Georgia special election

An 18-candidate debate shows how jumbled Georgia special election is

With Ossoff at the gates, Republicans try to fortify Georgia’s Sixth

Ossoff fights 'top-secret' attacks in Georgia special election

Republicans, Democrats target Ossoff in Georgia special election