When Republican presidential candidate Rick Perry formally declared his candidacy, one of the earliest questions was whether America was ready for another devoutly Christian Texas governor in the White House.

But a closer look reveals that the comparison is not only superficial, but in some ways off the mark. It is true that both men support a Texas-incubated philosophy of lower taxes and fewer regulations, but there is a history of coolness between them and of outright animosity between their advisors. That flows partially out of cultural differences, but it also reflects a fundamental belief on Perry's part that Bush, by expanding the reach and budget of the federal government, diverged from core Republican principles.

This big-government binge [in Obama's tenure] began under the administration of George W. Bush, Perry has said. He also admonished Bush for turning a blind eye to undisciplined domestic spending, according to the Washington Post.

Bush presided over a huge increase in domestic government spending, averaging an annual increase of about 5 percent. He also lent government a more active role in promoting educational standards through the landmark No Child Left Behind Law, and sought bipartisan support for his ultimately failed attempt at an immigration overhaul. He also coined the term compassionate conservatism, which he explained with the mantra of We have a responsibility that when somebody hurts, government has got to move.

Perry has derided that idea as an example of Bush capitulating on conservative ideals, writing in his 2010 book Fed Up that it implied that conservatism alone wasn't sufficient or worse yet, was somehow flawed and had to be re-branded.

The daylight between the two Texas governors, current and former, it about more than a clash of ideals between two men. It also parallels a broader shift in the Republican party, with Perry poised to become scion of a new era of obsessively spending-focused, ideologically combative Republicans. That movement is best embodied by Tea Party loyalists, a somewhat disparate group of voters that have nevertheless fueled Perry's supplanting Mitt Romney as current de facto frontrunner.

That means the 2012 election will help reveal the extent to which voters have adopted the GOP's rightward drift, or whether moderates shy away.

I think George Bush won crucial independent voters with his message of compassionate conservatism, top Bush campaign aide Mark McKinnon told the Post. I worry that today's Republican firebrand version of conservatism is dragging the party so far right that it will repel independent voters.