The volatile Republican presidential contest has provoked feverish talk in the media and the blogosphere about a brokered or contested convention in late August, when 2,286 Republican delegates gather in Tampa, Fla. Here's how those scenarios would unfold.

A brokered convention would see a new candidate -- someone other than Newt Gingrich, Ron Paul, Mitt Romney or Rick Santorum -- enter the remaining primaries or parachute in during the convention (if no existing candidate has secured a majority of delegates). In backroom deals, either based partly on the strength of his late primary performances or only on the discretion of party leaders, he would become the nominee.

A contested convention, on the other hand, would see no dark horse enter but none of the existing candidates arrive in Tampa with a 1,144 majority of delegates. Lots of wheeling and dealing would ensue, and after several ballots a nominee would emerge from the four current candidates.

Is either scenario likely? Let's put it this way: The odds are greater that there's life on Pluto than that the GOP has a brokered convention. And while there's a better chance of a contested convention, it's still highly unlikely.

Consider the calendar and the math. After Super Tuesday on March 6, a new candidate could still file for the Nebraska beauty contest, the Minnesota caucuses, and the primaries in New Mexico, California, Utah, South Dakota, New Jersey and Texas. Those eight contests have 519 delegates at stake: 238 awarded winner-takes-all, 241 split proportionally and 40 unpledged.

If a new candidate gets all the winner-takes-all delegates (unlikely since 222 in California and New Jersey are awarded by congressional district, not statewide), plus half those awarded proportionally, he still would have just 378 delegates of the 1,144 needed for nomination. At least two current candidates are likely to have far more. Why would they step aside for a newcomer?

Karl Rove is a former senior adviser and deputy chief of staff to President George W. Bush. He is a Fox News contributor and author of "Courage and Consequence" (Threshold Editions, 2010). To continue reading his column in The Wall Street Journal, click here.

Karl Rove joined Fox News Channel as a political contributor in February 2008. He also currently serves as a columnist for the Wall Street Journal. Mr. Rove helped organize the political-action committee American Crossroads. His latest book is "The Triumph of William McKinley: Why the Election of 1896 Still Matters" (Simon & Schuster, 2015). Follow him on Twitter @KarlRove.