Sen. Marco Rubio is reportedly considering whether to run for the Republican presidential nomination in 2016, with an announcement expected in a few weeks. One factor that must loom large in his deliberations is that former Florida Gov. Jeb Bush, with whom Rubio has long been allied, is also considering a run. Rubio probably can't run if Bush does.

Both men have their strengths. It would be better for conservatives, though, if Rubio ran and Bush bowed out.

Ideologically, there's not much difference between the two men. Both support "comprehensive immigration reform," including legal status for many illegal immigrants, a guest-worker program and stronger enforcement measures. Bush seems more adamant on the subject. Bush differs from Rubio in favoring "Common Core" standards for schools - but that's more of an issue for state and local governments than for the feds.

Bush's great advantage over Rubio is that he has been an executive, and a successful one. That's something that voters seem to like when hiring a president. But Bush is rusty. His last election was 12 years ago. He's been mostly absent from politics during the entirety of Barack Obama's presidency, and when he has popped up it has been to criticize other Republicans on taxes or immigration.

Bush's great disadvantage - the one that to my mind is decisive - is that he would make it impossible for Republicans to run the kind of campaign they need in 2016. The country has been unhappy with national politics for a long time, it is coming to the end of an eight-year presidency, and it is being asked to put the Clintons back in the White House.

Almost any Republican running in 2016 will therefore make the need to turn the page a major theme of his campaign. Rubio - who is young, vigorous and reform-minded - could do that. So could Wisconsin Gov. Scott Walker, or many other Republicans. Jeb Bush couldn't.

And that's why Republicans should hope he doesn't run, and doesn't keep more promising candidates from entering the race.

Ramesh Ponnuru writes about politics from a conservative perspective for Bloomberg News.