At 9:45 this morning, George H.W. Bush will open up his West Houston home to the press to make what is, for the octogenarian former president, a rare overtly political announcement: In the intra-Republican party fight for Texas governor, 41 has chosen U.S. Sen. Kay Bailey Hutchison over Gov. Rick Perry. He joins his close friend, longtime consigliere, and former White House chief-of-staff James Baker, who endorsed Hutchison earlier this week, and a long list of his son George W. Bush's closest associates in lining up behind the challenger to the incumbent. Hutchison has the public backing of former Vice President Dick Cheney, former Secretary of Education Margaret Spellings, and former Counselor to the President and communications director Karen Hughes, and she's being advised by former Deputy White House Chief of Staff Karl Rove.

Of all the prominent Bushies, Perry can claim only one outlier: Joe Allbaugh, who was chief of staff to Governor George W. Bush and the head of FEMA in 43's first term.

What's going on here? It's a question without a definitive answer and a subject that those in-the-know do not want to go anywhere near. Nearly every one of the two dozen sources contacted for this story refused to be quoted by name; several of those who went on the record saved their best material for after they went back off. But everyone with knowledge of the Bushworld-Perryworld divide had a theory. At least four emerged as plausible.

1. The predecessor-successor rivalry.

“This has a lot to do with what happens when you have succeeding governors. They have different teams,” said Bush 43 media strategist Mark McKinnon. “Perry is perfectly within his rights to establish his own identity.” Bush loyalists see their time in their governor's office as a golden age for bipartisanship — a time when they did right by Texas. Some of them believe Perry crassly squandered that compassionate conservative age by steering his administration and the state's politics farther to the right.

Perry's team sees that view of Bush's leadership as idealized; they blame President Bush for massive electoral losses and the tainting of the GOP brand. Perry, they insist, is the one who's truly led the state. They dismiss Hutchison and her Bushworld backers as "country-club Republicans," the phrase used by Perry campaign consultant Dave Carney in a recent New York Times Sunday Magazine story. The beneficiary of the bad blood is Hutchison, whose closer ties with Bush loyalists who worked in D.C. and more subdued personal style sits better with the family and its friends.

2. It's a moderate-conservative thing.

Most of the ink spilled about the GOP primary paints Perry and Hutchison as avatars in the battle for the soul of the GOP. It's not a bad theory to explain why the Bushies are backing Hutchison. The senator, while conservative by national standards, has been wedged into the "moderate" slot in Texas, with Perry occupying the terrain to her right. It would be natural, then, that Baker, the ultimate noblesse oblige Washington dealmaker, and Bush 41, the eldest of the elder statesmen and the biggest bulb in the Thousand Points of Light, find themselves aligned with the candidate who's offering a return to the days of the big tent.

"I would argue this is more about the electorate and where Texas has gone politically," says Ken Luce, who ran Perry's first campaign for agriculture commissioner.

Even back in 1998, the election year when many say the seeds of discord were first planted, Perry wanted to tamp down minority turnout as Bush's team wanted to expand it. Bush that year was simultaneously running for re-election as Texas governor and positioning himself for a national run. Perry ran alongside him for the lieutenant governor’s post, but Bush’s efforts to drive up Hispanic turnout forced Perry into a tough spot. Perry, who was in a much closer race against Democrat John Sharp, resisted efforts to court the Hispanic constituency for fear it would hand Sharp a slim victory. But Bush’s team had presidential ambitions on the line. The results worked out for both Republicans, but observers say hard feelings still remain.

“It’s a long-term play-out of this strain that’s been coming for at least twelve years,” said University of Houston political scientist Richard Murray.

3. It's not personal, it's business.

Perhaps this is all mercenary. Many of the political practitioners who went to Washington with Bush 43 have returned to Texas, and millions of dollars in lobbying, consulting and other lucrative employment in the political game are on the line if the governorship changes hands. The big dogs are back, but to regain power means ousting the current team that rules the town.

Members of Team Bush have already made significant gains in starting where they left off: on top. Hughes counts the Speaker of the Texas House as a client, advising him on communications; GOP sources say Rove is a friendly adviser to the Associated Republicans of Texas political action committee. ART, which was big when Bush was governor and dormant in the early aughts, is now restructuring. It will likely funnel millions of dollars to Texas House Republicans just in time for redistricting next session. Now their chosen proxy and personal friend, Hutchison, could be governor. Winning means windfalls; the consultants who win get hired by other prospective candidates.

4. It really is personal: The Bushies can't stand Perry.

This supposes the most personal rift in the Republican race for governor isn’t between the candidates at all.

“It’s visceral,“ Murray says. “The Bushies don’t like Rick Perry very much.“ The disdain for Perry is no secret among loyalists of George W. Bush, but never before have they had to choose sides in a fratricidal struggle. Now that two Texas Republicans are fighting for the same job, Hutchison’s become the beneficiary of more than a decade of bad blood.

A few incidents have fed the fire over the years. Some remember the 2001 Bob Bullock Museum dedication at which Perry kept referring to the new president as “George”. Or Perry’s criticism of the Bush administration’s handling of immigration policy.

Then there was the governor’s 2007 appearance at an Iowa house party for Rudy Giuliani. Perry told a living room full of Iowa Republicans that the President was “never, ever” a fiscal conservative. “Wasn't when he was in Texas … I mean, '95, '97, '99, George Bush was spending money."

He continued: “George was never a fiscal conservative. I think people thought he was."

The comments immediately rankled Bushworld, according to McKinnon. And there Perry went, calling the president “George” again.

That loose, stream-of-consciousness Perry style fed into a long-held Bushworld view of Perry as impolite and insincere. Sources close to Perry counter that the Bushies have long regarded themselves as superior and never fully appreciated Perry quietly working while lieutenant governor to keep controversial bills away from the then-governor’s desk.

"They're all Republicans"

It’s ironic, perhaps, that all these once-crucial cogs of the well-oiled Bush machine are now publicly backing a candidate who enjoyed her largest lead before she started campaigning. Bushies privately grumble over what they view as Hutchison’s lackluster and risk-averse campaign.

"They see the Rasmussen numbers [that show Perry leading by 10 points],” says Luis Saenz, who managed Perry’s successful 2006 campaign. “[The Bush] people are supposed to be the best. ... I think the message is that the Washington bosses don't matter as much anymore.”

Saenz is quick to note that whatever subterranean rift exists — for whatever reasons — won't bubble over. After all, they’re all Republicans, and Republicans are nothing if not disciplined at general election time. "Once March is over," Saenz says, "both sides will come together and start working toward a victorious November. Both sides have worked so hard to get the party to where it is."