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Already, organizations backed by the Tea Party were stirring interest in a primary challenge for Mr. Chambliss over his embrace of new revenues as a part of any comprehensive deficit package. Representatives Tom Price and Paul Broun, two Republican doctors and ardent conservatives from Georgia, had expressed interest in a possible challenge.

But without Mr. Chambliss in the picture, the Senate contest in Georgia could shape up to be a battle royale on the right. Other possible candidates could include Herman Cain, a failed presidential candidate, and Karen Handel, a former Georgia secretary of state who ran for governor in 2010 with the backing of Sarah Palin. Ms. Handel lost that contest but went on to a senior position at the Susan G. Komen for the Cure breast cancer foundation, where she championed a controversial move to withhold financing for Planned Parenthood cancer screenings.

In a statement, Mr. Chambliss took pains to say he did not fear losing a primary challenge.

"Lest anyone think this decision is about a primary challenge, I have no doubt that had I decided to be a candidate, I would have won re-election," he said. "In these difficult political times, I am fortunate to have actually broadened my support around the state and the nation due to the stances I have taken. Instead, this is about frustration, both at a lack of leadership from the White House and at the dearth of meaningful action from Congress."

Mr. Chambliss lifted his public stature in 2011 as one of three Republican senators in the "Gang of Six" hashing out a deficit reduction plan that the group hoped would capture broad appeal. Along with Senators Tom Coburn of Oklahoma and Mike Crapo of Idaho, both Republcians, Mr. Chambliss cemented strong bonds with Democratic deficit negotiators and ultimately embraced a framework that would include increases in revenues and cuts to entitlement programs to get the deficit in check.

But despite dozens of closed-door tutorials, secret retreats and symposiums, the Gang of Six failed to bring on board enough senators in both parties to force Democratic and Republican leaders to adopt its principles. It did elicit a strong backlash on the Republican right.

Democrats insisted they would make a run at his seat.

"Georgia will now offer Democrats one of our best pick-up opportunities of the cycle. There are already several reports of the potential for a divisive primary that will push Republicans to the extreme right. Regardless, there's no question that the demographics of the state have changed and Democrats are gaining strength. This will be a top priority," said Guy Cecil, executive director of the Democratic Senatorial Campaign Committee.

But in a mid-presidential term election, Georgia will present a steep climb for the Democratic Party.