Eliana Johnson reports for National Review Online on an interesting subplot in the race for the Republican presidential nomination.

Florida senator Marco Rubio (44) and Texas senator Ted Cruz (45) are both men of superhuman ambition who have put their personal advancement over virtually everything else, including, many would argue, loyalty, wealth, and family. Both were at least thinking about running for president from the time they arrived in the Senate. Their talent and their years-long focus on reaching the White House are reminiscent of Bill Clinton’s, and it’s entirely possible that the only thing standing between each and it, aside from another Clinton, is the other.

“You interview hundreds of candidates and a few stand out, and Rubio and Cruz stood out,” says Chris Chocola, the former president of the Club for Growth, the free-market group that endorsed both Rubio and Cruz in their Senate primaries. “They knew what they believed, they knew why they believed it, and they could articulate those beliefs.”

Their ascent to the top tier of the presidential field, where they have been trading barbs, is, for conservatives, a mark of astonishing success. Cruz is now viewed as the most conservative viable candidate, while Rubio is widely considered the most viable establishment choice (although he still has major competition from Chris Christie, among others). Yet this is a simplistic and somewhat misleading way to look at a prospective match-up between the two. Rubio was born of the tea-party movement and, during his Senate race, drove the liberal Charlie Crist out of the Republican party. That he is now considered a part of the Washington establishment says a lot about the transformation of the Republican party in the Obama era. “It’s a tremendous testament to what conservatives have been able to achieve,” says Mike Needham, the CEO of Heritage Action for America, a leading conservative-activist group.

Despite their obvious similarities, Rubio and Cruz have taken different routes to the top that reflect vastly different beliefs about what the GOP needs to do to win presidential elections again and vastly different aspirations for its future.