If Mitt Romney is going to be the Republican nominee, he needs the rest of the candidates to drop out -- just not yet. When Rick Perry said he'll "assess" his campaign and Michele Bachmann canceled her flight to South Carolina, aren't they suggesting they've given up hope of stopping the Romney machine? Not according to Wednesday's conventional wisdom. "The six words Mitt Romney doesn't want to hear from his opponents: 'I today announce I will withdraw,'" tweeted Ari Flesicher, former spokesman for George W. Bush. Romney benefits from having conservative voters split between a bunch of candidates, Politico's Maggie Haberman writes.

With Perry out, Haberman argues, "That opens up a nice swath of prospective backers for Santorum in South Carolina, the state where Romney needs a divided conservative field in order to have a strong shot." Republican strategist Alex Castellanos tells her, "The problem [for Romney] is that Santorum or some other conservative won’t have to outrun the bear, as the old joke goes, he’ll just have to outrun Mitt... That may not be impossible if a few conservatives drop out of the field and Mitt fails to expand his appeal." The National Review's Jim Geraghty says that Santorum could be the Mike Huckabee of 2012 -- unable to capitalize on a (near) victory in Iowa because he doesn't have the campaign organization. But if "the race comes down to Romney & Santorum, the former Pennsylvania senator will have access to funds from the grassroots. Perhaps not enough to go toe-to-toe with Romney, but enough to make it competitive."

Romney's problem might be the wrong people are dropping out. Jon Huntsman is luring away Romney's moderate voters in New Hampshire, Politico's James Hohmann writes. And Newt Gingrich seems to see his fight with Romney as a blood feud. He bitterly complained about the attack ads Romney backers ran against him, and promises to return the favor, telling the Des Moines Register's Jason Clayworth he's going to run ads in New Hampshire, South Carolina, and Florida. NBC News' Jo Ling Kent tweets this Gingrich ad running in the New Hampshire Union Leader Wednesday:

Yahoo's Holly Bailey points out that the anti-Romney vote remains strong despite the fact that the other candidates didn't attack him. Only 20 percent of negative ads in Iowa focused on Romney. Gingrich will certainly try to shift that balance going forward.