Sen. Lindsey Graham (R-S.C.) urged Republicans who are reportedly waiting until 2016 to run for president to consider getting off the sidelines for 2012.

Graham said Monday that the time was ripe to take on President Obama, and that any candidate with the ambition to be president should run.

"If you really decide to do this, now's the time," Graham said, noting speculation that a number of top GOP candidates are waiting until 2016. "If you think you should be president, it's not about timing, it's about ability."

"There's plenty of opportunity here for the Republican Party to win in 2012," the Palmetto State Republican said on conservative talker Laura Ingraham's radio show.

There are a number of Republicans considering running for president in 2012, including some of the GOP's biggest names, including former Alaska Gov. Sarah Palin, former Massachusetts Gov. Mitt Romney and former Speaker Newt Gingrich (Ga.).

But there are also a number of rising stars in the party who have passed on running for president this cycle, perhaps to run in 2016. Among them are New Jersey Gov. Chris Christie, Virginia Gov. Bob McDonnell and Louisiana Gov. Bobby Jindal, among others.

The conventional wisdom says that some of the candidates may be waiting for 2106 because they're hedging their bets about Obama's beatability in 2012. The president has the advantage of incumbency, and he's regarded as a formidable campaigner and fundraiser who won in 2008 with a broad electoral map.

Graham said that he didn't expect Obama to win North Carolina, Virginia or Indiana, as he did in 2008, and speculated that the president might be vulnerable in Wisconsin and Ohio, the latter of which is a traditional bellwether in presidential campaigns.

"Any sitting president probably has some built-in advantages, but this guy's incredibly exposed," Graham said.

The South Carolina senator didn't tip his hand as to which candidate he might back in a Republican primary (Graham spoke favorably in the past of South Dakota Sen. John Thune, who declined to run), but he did flag Christie for praise. Graham said that Republicans could win in 2012 "if our party will listen to Chris Christie on the economic side," and develops a strong contrast with Obama on national security as well.