Former governor and U.S. senator Zell Miller on Thursday endorsed Democrat Michelle Nunn in the U.S. Senate race, citing her bipartisan approach as an antidote for Washington gridlock.

But lest you Democrats get too excited: Miller said he fully intends to vote for Republican Gov. Nathan Deal, who is locked in a tough re-election bid with Democrat Jason Carter, grandson of the former president.

In a morning phone call from his Young Harris, Ga., home, the 82-year-old Miller cited Nunn’s work as the head of a major volunteer organization – founded by former President George H.W. Bush, a Republican.

“I have great respect for her dedication to public service, and her dedication to bipartisan results,” Miller said. “I think she shares a lot of characteristics with her father.”

Miller’s years as governor largely coincided with U.S. Sen. Sam Nunn’s final years in office. “I’ve known her since she was born,” Miller said. That was in 1966.

Despite his absence from the political scene, Miller still has a strong following in Georgia, especially among older and more conservative voters. What endorsements he’s made since his 2005 departure from the U.S. Senate have gone primarily to Republicans.

The Nunn campaign is taking immediate advantage of Miller’s endorsement with a TV ad blitz – to counter a $2.5 million televised attack by the National Republican Senate Committee, denouncing her as “Obama’s senator.” In the TV spot above, Miller says:

"I'm so angry about what's going on in Washington, partisanship over patriotism – they can't stop themselves. But we can stop them. Let's send Michelle Nunn to the Senate. She's a bridge-builder, not a bridge-burner."

Only after he had finished extolling Nunn did Miller emphasize that he would stick with a fellow mountaineer in the down-ticket race.

“I’m going to be voting for Nathan for re-election as governor,” said Miller, noting that the Republican had been saddled with serious economic problems when he took office in 2011.

“I respect the manner in which he’s conducted himself addressing those problems,” Miller said. Specifically, Miller cited Deal’s effort to shore up the lottery-funded HOPE scholarship program – which Miller established.

Miller’s split-ticket endorsement could make his backing of Nunn more valuable, not less – given that her Republican rival, David Perdue, can’t belittle it without also hurting Deal.

Miller’s gravitation toward Nunn rather than Carter could have its roots in the ‘70s, ‘80s and ‘90s, when Zell Miller, Sam Nunn and Jimmy Carter all wielded outside influence well beyond state lines.

Miller and Carter scarcely crossed paths when it came to state government service in the 1970s. Miller was first sworn in as lieutenant governor in 1975, as Carter exited the governorship and began concentrating on his run for the White House.

By contrast, Miller and Nunn, as governor and senior U.S. senator, respectively, overlapped for five years in the 1990s, said Steve Anthony, a Georgia State University political scientist who served as chief of staff to state House Speaker Tom Murphy during that period.

“[Miller] had a professional relationship with Nunn that he didn’t have with Carter,” Anthony said.

Gordon Giffin was a top aide to Sam Nunn before becoming U.S. ambassador to Canada. He is now chairman of the Michelle Nunn campaign. Here's a note Giffin sent describing some Zell Miller-Sam Nunn history:

Nunn and Zell ran together in 1990 as the first real "coordinated campaign." They were similar in that they were by nature independent in their perspectives -- get it done for those you represent and the country unrelated to party or ideology. In December 1991, they co-hosted one of the first major fund raisers for Bill Clinton at the Ritz in Atlanta. They agreed that a Southern moderate should lead the country. Today, they agree again....

Perhaps more to the point, while Miller and Carter may not have intersected that much in the '70s, their more recent shared history has been less than neutral.

Miller alienated many Democrats when he endorsed the re-election of President George W. Bush from the stage of the 2004 Republican National Convention.

Jimmy Carter was among them. Afterwards, in a two-page missive, the former president blasted Miller for his "rabid and mean-spirited speech.”

"By your historically unprecedented disloyalty, you have betrayed our trust," Carter wrote in the letter sent to Miller, who was then in his last months as a U.S. senator appointed by Gov. Roy Barnes.

Miller responded just as bluntly, in an AJC op-ed published after his presidential candidate won re-election:

"Jimmy Carter and Bill Clinton hummed the tune but never really sang the song, and that's why Democrat prospects have gone south in the South."

Miller dropped out of sight after he left the Senate, re-emerging only two years ago to endorse Doug Collins in his successful Republican race for Congress. The Collins campaign was managed by the former governor’s son, Bryan Miller.

Since then, Miller has quietly reached out to many of those he feuded with in the old days to make peace -- including Bill Shipp, the former AJC political columnist.  But we don't know that the Miller-Carter bridge has been rebuilt.