State Sen. Jason Carter’s run for governor was welcome news to many Democrats, but it could prove problematic for a party power broker known for his ties to Republican Gov. Nathan Deal.

Atlanta Mayor Kasim Reed’s alliance with the governor is the toast of the business community. After all, the two rallied behind the transportation tax and the need for a new Falcons stadium, and they tag-teamed a lobbying offensive to secure congressional approval to deepen Savannah’s port.

Their relationship is so cozy that Deal’s chief of staff donated to the Democrat’s successful re-election campaign, and so close that Reed, speaking after a business gala in May celebrating the duo’s partnership, predicted Deal would win re-election. Touting that potential victory, Reed — arguably among the most high-profile Democrats in the state — urged his party to focus instead on the open U.S. Senate seat.

Yet that friendship now puts the mayor, who sits on the executive board of the Democratic National Committee, in a delicate bind. As a rising star on the national stage, he faces pressure to toe the party line. But as a pragmatic politician who wants to burnish his bipartisan appeal, he also doesn’t want to jeopardize his relationship with the governor.

That could help explain the guarded statement Reed’s office released following Carter’s announcement. Reed praised Carter’s service in the Senate but stopped short of offering an endorsement of his gubernatorial bid.

“His candidacy, along with that of Michelle Nunn for U.S. Senate, is a sign of the growing energy and enthusiasm within the Democratic Party in Georgia,” Reed said. “I look forward to 2014.”

Unsurprisingly, Deal’s campaign is eager to remind voters of the powerful mayor’s past support.

“The wildly popular Atlanta mayor has said Governor Deal has done a great job and you should keep him there,” Deal spokesman Brian Robinson said. “That’s a pretty strong record to run on.”

Carter, for his part, reached out to Reed to inform him of the decision to challenge Deal before it was publicly announced. He sounded optimistic when asked during an interview whether he would enjoy Reed’s backing, but he didn’t say whether he expected a formal endorsement.

“Kasim Reed has done a great job of working across party lines,” Carter said. “When I’m the governor and when he’s the mayor, we’ll work together to continue doing that same thing, working with Republicans in the Legislature and across the state.”

Missing from his prediction, however, is what Reed will do to get him in office. Even if the mayor ultimately endorses his Democratic colleague, how far Reed goes to bolster Carter and discredit the opposition will be closely watched.

Robert Highsmith, Reed’s attorney and longtime colleague, doesn’t expect the mayor to endorse Carter. Highsmith, who stressed he’s not speaking on behalf of Reed, confirmed that doing so could hinder the bipartisan relationship the mayor and governor have forged on economic development. In a deeply red state, Deal is likely to win, he said, and thus supporting Carter is a political risk that may not be worth taking.

“I would expect the mayor to continue to be complimentary of Jason,” he said, “but I do not believe anything will happen in this campaign that would impede the very strong working relationship Georgia is benefiting from these two leaders.”

Steve Anthony, a Georgia State University political scientist, is among the analysts who say having the mayor’s support won’t make or break Carter’s chances anyway.

Reed’s political machine could help drive get-out-the-vote efforts in vote-rich Atlanta and its surrounding areas, he said, but “he isn’t going to affect anybody in South Georgia and Middle Georgia,” where voters tend to rebuff Atlanta mayors’ advances.

Any level of support Reed gives to Carter could provide a clue about the political future of the mayor, who also has often been considered a candidate for governor or other higher office. And in this case, doing little is saying something, Anthony said.

“If he withholds full-blown (support),” Anthony said, “is it because of his friendship with Deal or because he wants to keep the office open, so to speak, for himself four years from now?”

Chris Carpenter, a Democratic political consultant, says focusing on whether Reed’s support of Carter would harm his relationship with Deal misses the big picture: Seasoned politicians understand the nature of the game.

“They understand this is part of the process, and relationships certainly endure party politics and vice versa,” he said, noting both the mayor and governor should have a shared interest in improving Atlanta. “… I can’t imagine either of them would want to let party dynamics or party politics interfere with their respected goals.”