Former New York City mayor, media tycoon and gun control advocate Michael Bloomberg gave $350,000 to a pro-Michelle Nunn Super PAC last month, making him easily the biggest single benefactor to her campaign.

A new FEC filing from Georgians Together revealed the donation as the main engine behind the Super PAC's $400,000 ad campaign on Nunn's behalf.

Bloomberg had given the maximum $5,200 to Nunn's campaign earlier this year. Republicans have used it to cast her as a gun-grabber.

Other donors to Georgians Together, which is being guided by former Clinton White House aide Keith Mason, include Bill Clinton confidante Doug Band, who gave a comparatively paltry $2,500.

There is some history here. Sen. Sam Nunn and Bloomberg tooled around with the idea of a unity presidential ticket. Here's what our own Jim Galloway wrote in 2008 from Norman, Okla.:

The conclave of 16 centrist Republicans and Democrats --- some active but most retired --- also is intended to remind a public just tuning into the 2008 race for the White House that something was lost when political debate veered from the centerline of the American highway.

"Most people are in the middle of the road --- though they may stay in the left lane or the right lane, " argues Georgia's former Sen. Sam Nunn, a Democrat and one of the organizers of the session. "The very extreme activists are in the ditch on both sides, and that's where the money is."

Sandwiched between last week's caucuses in Iowa and Tuesday's primary in New Hampshire, the meeting on the campus of the University of Oklahoma --- its president, former Democratic Sen. David Boren, is also a sponsor --- is intended to pressure Republican and Democratic candidates for president to outline a middle path on tough issues like terrorism, the federal debt and health care.

The "or else what?" part remains deliberately vague.