Rick Perry and Ron Paul are both Republicans from Texas. Other than that, the two contenders for the Republican presidential nomination have little in common, and their shared party affiliation and state of residence has done nothing to bring them closer.
Whereas Perry is charismatic, smooth and has been a fixture of the Texas political establishment for decades, Paul is blunt, intentionally unpolished, and eager to highlight his frequent departures from party convention.
The two men can't even agree on whether they'd met before Perry's first presidential debate earlier this month. Paul said that they had not, while the Perry campaign begs to differ.
"They had met previously," Perry spokesperson Mark Miner told RealClearPolitics, noting that the Texas governor recalled hosting a meeting earlier in his term with the Texas congressional delegation, which he says Paul attended.
Paul has been particularly eager to contrast himself with Perry in style and substance over the past couple of weeks, and the Republican front-runner has not shied away from responding in kind.
After Perry entered the race last month, Paul denigrated his fellow Texan for being a "candidate of the week" and suggested that Republicans would sour on him once his record was scrutinized more closely. Then Paul released a TV ad in which he called his rival "Al Gore's cheerleader," in reference to Perry's 1988 endorsement of the Democrat.
Despite having bigger political fish to fry at the moment in the form of Mitt Romney, Perry engaged Paul directly in his first GOP debate by noting that the congressman had left the Republican Party in 1987 to run as a Libertarian candidate in the 1988 presidential race.
The two Texans got into it even further at Monday's CNN/Tea Party Express debate in Tampa when moderator Wolf Blitzer asked Paul whether Perry deserved credit for the state's job growth.
"I'm a taxpayer there," Paul said in immediately personalizing his answer. "My taxes have gone up. Our taxes have doubled since he's been in office. Our spending has gone up double. Our debt has gone up nearly triple. So no, and 170,000 of the jobs were government jobs, so I would put a little damper on this, but I don't want to offend the governor because he might raise my taxes or something."
Paul's eagerness to take Perry on -- and Perry's willingness to oblige him -- has created a dynamic in which the three-term governor may be in danger of taking his eye off the ball, with Romney standing by and watching it unfold.
Jim Henson, director of the Texas Politics Project at the University of Texas, said that one consequence of GOP hegemony in Texas is that some of the state's most deep-seated political antipathies are between Republicans.
"From 30,000 feet, they would seem like natural allies, but from the beginning, Paul's presence has been an irritant to the Perry campaign," Henson said. "I think part of the ethic of the Perry campaign is that they like a good fight. Up to this point, they've been good at it, and it's part of their public and self-image that they don't shy away from a fight. They're certainly willing to declare victory and exit the battlefield at the most advantageous point, but the campaign's approach is reflexively scrappy."
Paul's eagerness to take Perry on so directly is a departure from the congressman's 2008 strategy, when he focused relentlessly on delivering his own message consistently and emphatically, rather than emphasizing his opponents' flaws.
And so far, Paul's efforts appear to be having an effect, as he has been a significant factor in the debates rather than a mere sideshow.
Perry critics have noted that while the Texas governor is typically comfortable when he is on the attack, he has at times proven less sure-footed when opponents have put him on the defensive. And indeed, his tendency to "punch down," rather than pivot away from lower-tier candidates, has been on display in the two debates thus far.
Tea Party activist Debra Medina, who twice shared a debate stage with Perry and Sen. Kay Bailey Hutchison during the 2010 Texas gubernatorial primary, witnessed firsthand Perry's discomfort with being challenged directly by a candidate who may not ultimately defeat him but is nonetheless eager to make him squirm.
"Certainly I'd say there's a huge divide between who Rick Perry is in fact and who Rick Perry is portrayed to be, and that's what Ron Paul is trying to demonstrate," Medina, who is a Paul supporter, told RCP. "So now he's in front of seven other Debra Medina's saying, 'Wait a minute, Governor, that's not what's going on out there.' "
Perry's decision to respond directly to, rather than deflect, Paul's jabs seems a significant risk. But the Perry campaign says that just because the GOP front-runner is willing to engage with Paul does not mean he is in danger of falling off message.
"Some candidates, the only way they can get attention is to make outlandish comments, and the only way they can get into the news cycle is to say something that is not true. But to get attention, they'll say it," Mark Miner said of Paul. "Everybody at the debates has been attacking the governor, including the moderators, so it seems to be a game plan by the other candidates, but it's not going to change our strategy or what we're doing. The governor's going to continue to talk about his issues, and when there's misinformation or factually incorrect comments made, he'll stand up to correct those comments."
Still, Paul's keenness to lock horns with his fellow Texan poses a clear long-term challenge to Perry, since the congressman is likely to remain in the race deep into the nominating cycle, no matter how Paul fares in the early voting contests.
In Iowa, where recent surveys show Paul polling in the double digits, the libertarian-leaning candidate is likely to join Minnesota Rep. Michele Bachmann in challenging Perry from his right flank over the controversy surrounding his 2007 executive order mandating that young girls be vaccinated against human papillomavirus (his former chief of staff was a lobbyist for Merck, which makes the vaccine Gardasil).
"Congressman Paul being from Texas and being someone who deeply respects states' rights, takes the governorship very seriously, so things like raising taxes and the Gardasil issue are things that really hit home for him," said A.J. Spiker, Paul's Iowa co-chairman. "Because of his belief in constitutionally limited government, crony capitalism is something that's always been offensive to Congressman Paul."
Paul alone may never get enough airtime to put a significant dent in Perry's armor in the early voting states. But a sustained and unofficially coordinated assault on Perry that combines his weight with that of Bachmann and former Pennsylvania Sen. Rick Santorum could give Perry another reason to worry about more than just Mitt Romney going forward.
Scott Conroy is a CBS News consultant and reporter for RealClearPolitics.