Not long ago few thought Mitt Romney could win both the very conservative Iowa caucuses and then the quirky, slightly contrarian New Hampshire primary. If he did, most assumed he would have a lock on the Republican nomination. For understandable reasons: No other GOP presidential candidate in an open race has achieved back-to-back victories in these first two contests.

By this time next week, we'll know if Mr. Romney is 2-0. If so, he becomes the prohibitive favorite.
The other big Iowa winner is former Pennsylvania Sen. Rick Santorum. Iowa does winnow the field (as it did with Wednesday's departure of Congresswoman Michele Bachmann). But it also gives unheralded contenders like Mr. Santorum a chance to jump into the spotlight. And in spectacular fashion, he did. He essentially tied the GOP front-runner, leap-frogging the governor of the second-largest state (Rick Perry) and the former speaker of the House (Newt Gingrich).

Mr. Santorum shouldn't kid himself; he faces huge obstacles. He's spent a year making Iowa his second home. Now he's in less friendly, less familiar terrain. He hasn't had to endure withering scrutiny but will shortly. His chief opponent has tremendous organizational and financial advantages and has been through the rigors of a presidential primary race. Still, Mr. Santorum has a shot, and that's all he could have hoped for.

Looking ahead, he has to hope New Hampshire pays attention to what happens in Iowa (it traditionally hasn't) and that he can rapidly cobble together money, organization and a message to compete in January's primaries in South Carolina and Florida, as well as the Granite State. Until yesterday, Mr. Santorum hadn't been in New Hampshire in a month, South Carolina for two, and Florida hardly at all.

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.