Sen. Saxby Chambliss (R-Ga.) waits to speak with reporters on Capitol Hill in November. On Friday, Chambliss announced that there would be no re-election for him. (Cliff Owen/AP)

The trio of Southern gentlemen came to the Senate together in 2003, the leading edge of a renegade Republican class set on shaking up the chamber’s staid ways and aggressively promoting the Bush White House’s conservative agenda.

Ten years later, Sens. Lamar Alexander (Tenn.), Saxby Chambliss (Ga.) and Lindsey O. Graham (S.C.) are now establishment dealmakers and elder statesmen — roles that earn them respect in Washington but could lead to tough challenges from fellow Republicans when they run for re-election next year.

On Friday, Chambliss announced that there would be no re-election for him, opting for retirement over another run that was certain to include a heated primary challenge, possibly from several candidates. Chambliss took pains to say that he would have won and instead cited Washington “gridlock” as his reason for retiring.

Regardless, Chambliss’s departure is another blow to the pragmatic wing of the Senate, with a lineup of potential successors all hailing from the staunchly conservative camp of the Georgia GOP.

Chambliss’s successor is likely to contribute to a rightward movement over the past four years that has made the ranks of Senate Republicans more conservative, but also led to repeated political disappointment. A handful of 2010 and 2012 Republican primaries produced nominees who bungled their way to general election defeat, when victory once appeared certain.

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What happens with the other two Southerners could go a long way to determining the ideological makeup of the Senate Republican caucus.

Alexander and Graham are both running, raising money and appearing throughout their states. Alexander, a former two-term governor and U.S. education secretary, has the stronger footing for the moment, having locked up the endorsements of his state’s GOP congressional delegation and every prominent Republican state official. Graham has no prominent challenger yet, but Palmetto State Republicans are sizing up the race trying to decide if he’s ripe for a challenge.

That Alexander, Chambliss and Graham have found themselves in this situation, a decade after debuting as rabble rousers who helped return the chamber to GOP control, is the latest demonstration of how much the Republican Party has changed. Its voters more than ever demand a confrontational tone and in-your-face tactics, the sort of behavior that they have shied away from.

“The big change is in terms of strategy and tactics,” said Stuart Rothenberg, editor of the nonpartisan Rothenberg Political Report, noting that the three incumbents are all fairly conservative in their policy positions. “The war has changed. Republican voters want every fight to be hand-to-hand combat. They don’t want to give any ground.”

Alexander rejected the idea that the trio had “gone Washington” as they each became more powerful. “I know my way around here. We’re each finding our niche, and that’s pretty normal after 10 years,” he said in a recent interview.

Before his Friday announcement, Chambliss had been viewed as the most vulnerable Republican incumbent to a challenge from within. His apostasies to the new Republican posture were numerous in recent years, most prominently being his close partnership with Sen. Mark Warner (D-Va.) in an effort to craft a bipartisan package of tax hikes and entitlement cuts to rein in the federal government’s $16.4 trillion debt.

He openly flouted the idea that all Republicans had taken a pledge from Americans for Tax Reform, the anti-tax outfit headed by activist Grover Norquist, and vowed to push ahead with Warner in the face of political heat.

“I care more about my country than I do about a 20-year-old pledge,” Chambliss told an Atlanta TV station late last year. “If we do it his way then we’ll continue in debt, and I just have a disagreement with him about that.”

Chambliss even spoke at a fundraiser for Warner, the sort of bipartisan gesture that rarely happens in today’s hyper-partisan Senate.

That tone led several members of the state’s congressional delegation, including conservative Reps. Tom Price and Paul Broun, to consider challenging him, along with other prominent Georgia Republicans.

In his retirement announcement, Chambliss declared he had “no doubt . . . I would have won re-election.” However, he made clear that hope was fading for winning the kind of bipartisan deal he and Warner had been searching for, making it not worthwhile to fight through a brutal campaign for a third six-year term.

“I don’t see the legislative gridlock and partisan posturing improving anytime soon,” he said.

Now, a wide-open primary is under way and the favorites all hail from the party’s most conservative wing.

“The retirement of Senator Chambliss opens a door for continued tea party growth in the U.S. Senate. Many people in the tea party movement here in Georgia felt Chambliss was tired and unwilling to fight,” Tea Party Express Chairman Amy Kremer, a Georgia native, said after the announcement.

Alexander appears to have followed a trail blazed by Republican Sens. John McCain (Ariz.) and Orrin G. Hatch (Utah), both of whom faced potentially stiff primary opponents, in 2010 and 2012 respectively, but ran very aggressive campaigns that thwarted their challengers. His key has been maintaining a very visible presence in Tennessee, where tea-party activists have had limited success in statewide races.

Alexander’s diagnosis of defeated Republican incumbents such as former senators Robert F. Bennett (Utah), who lost in a primary challenge in 2010, and Richard G. Lugar (Ind.), who similarly lost in 2012, is that they had lost visibility among local activists. “They lose because they have drifted away from the people,” Alexander said, adding that he maintains an “intense and intact relationship” with local party officials.

Like Chambliss, Alexander has recently focused on bipartisan dealmaking, working with the Georgian on debt issues and helping secure a rules reform pact last week with Democrats. He even quit his leadership post in 2011 so that he could free himself to work in a more bipartisan fashion.

“I don’t miss it at all,” Alexander said, smiling mischievously after he helped secure the rules compromise. “I like this kind of leadership.”

According to Rothenberg, Graham falls somewhere between Alexander and Chambliss in terms of vulnerability to a conservative challenge. He entered Congress in 1995 as a foot soldier in the Newt Gingrich GOP revolution, helping shut down the federal government and helping lead the impeachment trial against President Clinton as a House member. When he arrived in the Senate, he helped lead the fight to forbid filibusters on George W. Bush’s judicial nominees and advocated a partial privatization of Social Security.

Yet he’s also supported President Obama’s Supreme Court nominees, worked with Democrats to curtail terrorist interrogation techniques, and supported more tax revenue as part of debt compromises. This comes as South Carolina has become the unofficial capital of the tea party, electing a governor and a House delegation almost entirely from that activist wing. Former senator Jim DeMint (R-S.C.) helped defeat many establishment favorites in recent Senate GOP primaries, and several members of the South Carolina congressional delegation are weighing a challenge to Graham.

Each of the three states — Tennessee, South Carolina and Georgia — have tilted so far toward Republicans in the last two decades that Democrats have little to no chance of challenging for those seats in a midterm election. Then again, senior Democratic strategists on Friday began picturing what the primary process would look like for Republicans, searching for candidates who would appeal to the middle in case an unelectable conservative won the nomination.

Rothenberg said the trend in GOP primaries suggests Democrats might as well find at least somewhat credible nominees in Georgia and South Carolina. “Everything is all or nothing in Republican politics,” he said. “And increasingly now it’s nothing.”