he Senate on Tuesday voted 89-8 to pass a bill extending the Bush tax cuts for all but the wealthiest Americans. The legislation was hailed by leaders of both parties as a bipartisan effort to prevent across-the-board tax hikes, and represented the first time in 20 years that the GOP has agreed to allow tax rates on anyone to rise. But five Republicans were not on board, most conspicuously Sen. Marco Rubio, the rising star from Florida who is widely seen as a potential candidate for the 2016 Republican presidential nomination. "Rapid economic growth and job creation will be made more difficult under the deal reached here in Washington," Rubio said in a statement, arguing that layoffs would ensue from raising taxes on the wealthy and small businesses.

If there is a common Achilles Heel for senators aspiring to become president, it is their voting record. Democratic and Republican primaries can be purist affairs, and compromises on core ideological beliefs do not play well with base voters. Hillary Clinton's vote to authorize the Iraq War, for example, doomed her campaign against Barack Obama. Indeed, Rubio, who like Obama was a celebrity before setting foot on Capitol Hill, may be wise to follow Obama's example, making his tenure in the Senate as short, sweet, and fingerprint-free as possible.

It appears that the Republican leadership agrees. Party unity was essential on the fiscal cliff vote, since a large defection could have alarmed GOP members and scuttled the deal. However, a few senators were allowed to keep their anti-tax position immaculate, and it's no coincidence that Rubio was one of them. He is one of the party's greatest hopes, and it would be a shame to see his 2016 candidacy go down in flames in the primary over a single vote.

Some conservative commentators are disappointed in Rubio's no vote. "Apparently, his advisers have convinced him that irresponsibility is the road to the White House," says Jennifer Rubin at The Washington Post. "It is not the first time that he has chosen to play to the right-wing peanut gallery, showing a troublesome timidity in the face of future primary votes." However, others disagree, underlining the perils of going against party orthodoxy. "Like TARP in 2008, this vote will separate the conservatives from the Republicans," says Erick Erickson at Red State.

With that kind of pressure, it wouldn't be surprising if the Republican leadership allowed Rubio to vote anyway he liked over the next four years, creating a one-man bubble to protect their star from the contamination of Washington deal-making. On the flip side, it will be interesting to see in the coming months how much freedom Rubio is given to reach a deal on immigration reform. The Cuban-American is expected to spearhead the party's approach to the issue as it tries to make gains with Latino voters, but it's an area that could get him into trouble with the base.