Whatever their differences, Rick Perry has at least one thing in common with Barack Obama: He apparently doesn't think much of George W. Bush, at least politically.

Going back at least two years, Perry has criticized his predecessor in the Texas Governor’s Mansion, whom he served alongside as lieutenant governor, for not being conservative enough. In a living room speech given to Iowa Republicans while he was stumping for then-presidential candidate Rudolph Giuliani, Perry complained, “’95, ’97, ’99, George Bush was spendin’ money. George has never, ever been a fiscal conservative … and I think people thought that he was.” Footage of Perry’s comments was posted onto the internet and instantly irked Bush loyalists.

In January, a roster of high-profile Bushies with long memories — including former vice president Dick Cheney, former White House Chief of Staff James Baker, former Secretary of Education Margaret Spellings, former Counselor to the President and communications director Karen Hughes and former Deputy White House Chief of Staff Karl Rove — paid Perry back in kind by publicly backing U.S. Sen. Kay Bailey Hutchison in her unsuccessful bid to swipe the Republican nomination for Texas governor. The interparty battle pitted the Bushes, who Perry’s chief consultant, Dave Carney, contemptuously described as “country club Republicans,” against a rising Tea Party movement that Perry embraced in its infancy.

Most recently, as the two men have embarked on concurrent cross-country book tours — a coincidence of timing, both camps say — Perry has returned to his familiar critique. In his anti-Washington manifesto Fed Up!, he excoriates Bush’s “compassionate conservatism” for sending the wrong message: that unqualified conservatism was “somehow flawed and had to be rebranded.” In interviews promoting the book, Perry has attacked his predecessor’s “big government overspending,” citing two of Bush’s signature achievements, the Medicare drug benefit for seniors and the No Child Left Behind education law, as examples of burdensome federal behemoths.

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“[Perry]’s just more conservative,” Carney says. “He’s fiscally more conservative. He’s socially more conservative. I don’t think anyone’s questioning that.” Carney insistes it’s a “total misread” to see Perry’s book as an indictment of Bush.

Team Bush has responded with variations on a simple theme. “It's not surprising that Perry is trying to eliminate the artificial barrier to entry [onto the national stage] by separating himself from President Bush,” says Mark McKinnon, Bush’s longtime media strategist. “It is surprising, and unfortunate in my view, that he's chosen to step on the legacy of the President Bush to do it.”

Theories abound as to the origin of the rivalry between Bush and Perry: predecessor-successor tension, questions over which man is a “true” conservative, simple differences in style. Whatever the reason, “there’s certainly no love lost between those two men,” says Bruce Buchanan, a political scientist and presidential scholar at the University of Texas.

Unlike Bush, an East Coast-bred and prep-school- and Ivy League–educated heir to Republican royalty, Perry was born on a farm in rural West Texas and famously graduated from Texas A&M University. The brush-clearing, straight-talking Texas persona that Bush successfully honed on his path to the presidency arguably fits a bit more naturally on Perry, who inherited the statehouse when Bush moved to the White House and has since become the state’s longest-serving governor.

“Texans … elect folks like me,” Perry writes in Fed Up! “You know the type, the kind of guy who goes jogging in the morning, packing a Ruger .380 with laser sights and loaded with hollow-point bullets, and shoots a coyote that is threatening his daughter’s dog.”

Beyond personal backgrounds, they are each the product of specific political times. “Their circumstances are different — let’s be direct about that,” says James Huffines, a Perry friend and ally and who has served as finance chairman of his campaigns.

During Bush’s time as governor, Democrats controlled the Texas House and Senate, requiring that he work with the majority party to pass his signature proposals: tort reform, education reform, juvenile justice reform and welfare reform. “When I was there, the [Republican] governor and [Democratic] lieutenant governor and I had breakfast every Wednesday morning,” says former Democratic Speaker Pete Laney, whose years leading the Texas House overlapped Bush’s tenure as governor.

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By the time Perry took over in 2000, the comity of Bush’s day was swept away by an indelibly red wave that led to the takeover of the House by the GOP for the first time since Reconstruction. This both allowed and required Perry to tack further to the right politically and preside in a way that stiff-armed Democrats in order to appease social conservatives. “You’ve got a situation now where opposing groups aren’t even speaking to each other,” Laney says. “My relationship with Perry wasn’t the same with Governor Bush, because Perry chose it to be that way.”

Bush himself has been noticeably silent about Perry’s jabs, just as he has been about those of his other successor. “When you see Bush on the national scene, he refuses to say anything negative about President Obama or the past Congress, when he has had plenty of opportunity to do so,” notes Adam Goldman, a veteran Bush staffer who worked on his gubernatorial campaigns and as a White House aide. But silence can speak volumes. In Decision Points, Bush makes not a single mention of Perry — though he does take pains to criticize the hyper-partisan redrawing of Texas’ congressional and legislative districts in 2003, an effort helmed by Perry, Republican Speaker Tom Craddick and U.S. House Majority Leader Tom DeLay.

How long the uneasy peace holds is anyone’s guess, as the tension is entering a new phase. Like Bush before him, Perry now finds himself parlaying the Texas governorship into a prominent position outside of Texas. He recently ascended to the chairmanship of the Republican Governors Association, and speculation is mounting — over the adamant denials of Carney and other aides — that he may be planning a campaign for president of his own, which would provide more of an opportunity for compare and contrast.

“Bush is instinctively more of a pragmatist than Perry is,” Buchanan says. “Right now, Perry perceives it as in his interest to be the opposite of that.”

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