Mitt Romney's big (though hardly unexpected) win in New Hampshire's Republican presidential primary is the day's top political news. But Tuesday's Granite State vote was "only the appetizer to South Carolina's main course" on Jan. 21, says Chris Cillizza at The Washington Post. Here, four reasons why the next GOP nominating contest is the one that will really count:

1. It's all or nothing for Gingrich and Perry
Romney is "likely to spend the next 10 days fending off attacks from several of his opponents who see the Palmetto State as their last stand," say Michael Falcone and Amy Walter at ABC News. South Carolina is a "must-win state" for Newt Gingrich, and he's already trying to "bring the pain" with TV ads calling Mitt's stint as Massachusetts's governor "pro-abortion." Rick Perry, in the same boat, will inevitably blast Romney, too, on everything from social issues to Mitt's corporate-buyout days at Bain Capital. Such nothing-to-lose attacks may cost Romney votes.

2. South Carolina is less disposed to favor Mitt
In many ways, Mitt is sitting pretty after his "historic sweep of the nation's first two contests" in Iowa and New Hampshire, says Dave Wedge at the Boston Herald. But, unlike New Hampshire, South Carolina is a "conservative hotbed" where hard-right Christians are skeptical of Romney, a relatively moderate Mormon. "The biggest knock on Romney has been that he's not a true conservative, and that's a theme Gingrich, former Sen. Rick Santorum, and others are likely to try and hammer home."

3. But Romney could also wrap up the nomination here
A Romney win in South Carolina, says Cillizza, "effectively ends the GOP nomination fight. A loss by Romney likely means a protracted primary fight that continues through Super Tuesday on March 6." Romney's the choice of establishment Republicans, but the title of "consensus conservative candidate" remains "very much up for grabs." Conservative activists are in a "near-panic," say Peter Wallsten and Karen Tumulty, also in the Post. They know that if they can't pick one conservative to rally behind, the nomination is Romney's.

4. South Carolina always picks the winner
South Carolina Republicans have a saying: "Iowa picks corn, New Hampshire picks campaigns' pockets, and South Carolina picks Republican presidents." And that's "not just a catchy phrase," says Anna Fifield at Britain's Financial Times. "South Carolina has voted for the eventual nominee in every Republican primary since 1980." That alone arguably makes the state a bigger deal than New Hampshire. Plus, South Carolina primaries are "famously vicious." Stay tuned.