The next major event in the 2012 presidential race will come when Mitt Romney selects a running mate. The effect could be seismic -- recall the way Sarah Palin's emergence briefly boosted John McCain's 2008 hopes, injecting his listless campaign with a sense of freshness and buzz before raising doubts about his penchant for rolling the dice. Or it could be subtle: While Joe Biden's foreign policy experience and ability to communicate with blue-collar voters are sometimes touted, few would argue his selection four years ago shook up the race, even if it did dash the final hopes of Hillary Clinton supporters.

Where things stand with Romney's thinking is anyone's guess; he has deputized a senior adviser, Beth Myers, to assess the field, and has otherwise been coy about his thinking on the process. A rising generation of Republican stars gives Romney a wide array of personalities to choose from. But there's one problem: Some of those rising stars may shine a little too bright, threatening to overshadow Romney in the process.