Following crushing setbacks that could have sidelined their respective careers, Republican Sens. Trent Lott (Miss.) and John McCain (Ariz.) have put aside long-standing differences and become leading architects of each other’s political resurrections.

In the process, Lott and McCain have created an influential network of Senate Republican allies who by circumstance or design are loyal to them both. In fact, many of Lott’s strongest devotees also are backers of McCain’s 2008 presidential bid, and vice versa.

When Lott plotted a return to the GOP leadership as Minority Whip in the fall, McCain served as one of his most eager promoters and helped count votes in the Mississippian’s campaign. And it was Lott who more than a year ago became one of the first Senators to back McCain’s bid for the presidential nomination and has since become one of the Arizonan’s top Senate surrogates.

“They are sort of like ham and eggs,” observed Sen. Lindsey Graham (R-S.C.).

But it wasn’t always that way. Lott, the consummate leadership deal-maker, and McCain, long the meddlesome maverick, have engaged in bitter legislative battles over the years about high-profile issues such as campaign finance and earmark reform.

The two parted ways for a time after Lott successfully campaigned for GOP Whip in 1994 and moved for the first time into the Senate leadership. And in 2000, Lott opted to back then-Texas Gov. George W. Bush for the presidency over his Arizona Senate colleague.

“I didn’t think the time was right for John then,” Lott explained recently. “I thought that George W. Bush was the right man for the job at that time. But [McCain] has come back, better and stronger.”

McCain doesn’t dispute Lott’s assessment, admitting he may not have been the best candidate during his earlier White House run: “First, I certainly didn’t have the experience that I have now. And secondly, America was at peace in the 2000 campaign. [The Sept. 11, 2001, terrorist attacks] changed everything.”

Certainly, times have changed. Lott has spent months helping court Congressional and build national support for McCain’s 2008 White House bid. He has advised McCain, spoken on his behalf and helped him set his campaign priorities.

Similarly, it was McCain who helped persuade Lott to not only run for a fourth term in 2006, but to make another play for the Republican leadership by seeking the No. 2 Whip job. McCain was a key whip in that race for Lott, who eked out a one-vote win over Sen. Lamar Alexander (R-Tenn.).

“We understand each other,” McCain said. “When you know somebody for such a long period of time, you either grow closer or more distant. We’ve become closer and closer over the years.”

Lott said both men share conservative ideological backgrounds and have been tested “warriors” under the glaring spotlight of the political stage. Lott said he’s so fervently behind McCain’s White House bid because he “wants to win the presidency” and believes the veteran Arizonan “is a very thoughtful leader possessing the kind of leadership qualities and character you need to be president.”

“There’s no quid pro quo there,” Lott said.

McCain’s and Lott’s backgrounds have much in common. They share a Scottish heritage, and both families’ genealogy and political connections trace back to the 1800s in Carroll County, Miss.

They are both creatures of Congress — Lott began in the House in 1973 and moved to the Senate in 1989, while McCain started his brief House tenure in 1983 and was elected to the Senate in 1986.

“Even when we’ve fought like cats and dogs, we’ve always kept our relationship — and let me tell you, it was testy at times,” Lott said.

“We’ve had some of the best fights in the United States Senate,” McCain offered.

Friends of the two men say both Lott and McCain have matured somewhat in recent years and developed a better understanding of one another following McCain’s unsuccessful first bid for the White House and Lott’s fall from leadership in 2002. Lott was forced out as Majority Leader on the heels of remarks that were perceived as racially insensitive at the 100th birthday of the late Sen. Strom Thurmond (R-S.C.).

Sources say it was then that Lott shared a common experience with the oft-rebellious McCain — understanding what it’s like to be isolated from and ostracized by your colleagues.

“Trent Lott’s wilderness years made him appreciate John McCain because he stayed with him during difficult times and Trent Lott saw a side of political life that he didn’t see before,” Graham said. “They’ve grown to really enjoy each other’s company.”

In his four years as a rank-and-file Senator, Lott returned to legislative deal-making, and had the freedom outside of the confines of leadership to speak his mind and even take on President Bush and members of his own party. Lott and McCain, meanwhile, found some areas of agreement, from their support for the Iraq War to certain aspects of lobby reform to fiscal discipline.

“They both learned a lot,” noted a former Lott staffer. “People who are competitive or who have a drive don’t like to lose. You can do one of two things: You can learn from your mistakes, or you can sulk and walk away. They both learned from their mistakes.”

“There’s something about people who were dealt a bad hand and overcome adversity and come back from that,” added Sen. John Thune (R-S.D.). “It’s quite a bond that’s been built.”

Thune counts himself among those Senators in both the Lott and McCain political camps. The conservative South Dakotan is not only Lott’s chief deputy whip, he also is a newly announced backer of McCain for President.

McCain has yet to announce all of his Republican Senate endorsements, but among those already publicly in his camp are several GOP Members who aided Lott’s quest for the Minority Whip post. They include Thune, Maine Sens. Olympia Snowe and Susan Collins, and Virginia Sen. John Warner.

More close Lott allies are expected to declare their support for McCain in the coming weeks.

“There is a natural overlap in these two groups,” said one Republican Senator, speaking on the condition of anonymity.

This Senator said Lott and McCain have cultivated their influence in part by paying special attention to nurturing relationships with more junior Senators. Lott served as a mentor to those his junior over Senate rules and procedures, while McCain carried a policy portfolio of fiscal restraint that appealed to the up-and-comers, the Republican Senator said.

“There were a number of areas where those alliances proved to be mutually beneficial,” the Senator said.

Warner, who also has had his friction with Lott at times over the years, said his shared support for both Lott and McCain is simple: “There’s a common chemistry in both of them, and that’s strong leadership. Without being presumptuous, I assume that’s one of the reasons they admire each other. There’s a common desire of Senators to form strong leadership.”

Warner was one of the leading Senators who, along with McCain, helped form the “Gang of 14” that came together in 2005 to try to avert a showdown over Bush’s judicial nominations. Lott was an original leader in the group but later stepped aside, leaving McCain and Warner to take the helm.

Snowe, who has known both Senators since the trio served in the House, said it is no accident that Lott and McCain have forged such a bond given their long track record together. After two-plus decades in the House and Senate, the duo has developed a level of trust that’s all but unmatched on Capitol Hill these days, she said.

“That foundation is so crucial, and it’s what gave impetus for Trent supporting John McCain for the presidency and for John to help Trent in his bid for Minority Whip,” she said.

“There’s a mutual bond there that supercedes any disagreements they’ve had over the years.”