Thursday morning was not a good one for Mitt Romney.

View Photo Gallery: A look at the former Massachusetts governor now seeking the GOP presidential nomination.

The former Massachusetts governor’s campaign started off on offense. His campaign announced the endorsement of Sen. Rob Portman (R-Ohio), a former Office of Management and Budget director and rising GOP star.

And Romney’s camp kept its sights trained on President Obama, releasing a Web video and penning an open letter to the president criticizing his leadership ahead of his scheduled trip to Florida.

“Your policies have failed, and not only in Florida, but across the nation,” Romney wrote.

But then things went off track for the former Massachusetts governor and GOP frontrunner.

First there was the news that Romney had not won the first-in-the-nation caucus state of Iowa after all.

The state Republican Party announced early Thursday morning that former senator Rick Santorum (R-Pa.) was leading Romney by 34 votes in the Hawkeye State, although the results from eight precincts were still pending.

And then there was an even more potentially problematic development for the Romney camp: Texas Gov. Rick Perry (R) announced he was dropping out of the race and endorsing Romney’s rival, former House speaker Newt Gingrich (R-Ga.).

The news came one day after a CNN/Time/Opinion Research poll showed Gingrich chipping away at Romney’s lead in South Carolina: in the latest survey, which had a 4.5 percentage point margin of error, Romney takes 33 percent to Gingrich’s 23 percent among likely GOP primary voters. That’s narrower than Romney’s 18-point lead in early January.

Taken together, the developments mean that the heat will be on for Romney at Thursday night’s CNN/Southern Republican Leadership Conference debate in Charleston, S.C.

In the most recent CNN poll, six percent of likely primary voters backed Perry. If all of those supporters moved to Gingrich, that would put the former House speaker at 29 percent in South Carolina – within the margin of error for a victory over Romney.

The fact that Romney now technically is not gunning for a three-in-a-row victory in the early nominating contests could also take some momentum out of his Palmetto State push, opening a window of opportunity for his rivals to make the case that Romney is not his party’s inevitable nominee.

The silver lining for Romney: some of Perry’s top backers have already defected to the former Massachusetts governor’s camp. And some of Perry’s supporters may opt for Santorum over Gingrich, preventing social conservatives from coalescing around a single candidate in the race.

There’s also the news that Gingrich’s former wife, Marianne, is coming forward with some of the details of her years with the candidate, alleging that Gingrich asked her in 1999 for “an open marriage.”

The interview could be a game-changer for the former House speaker, and it will be worth watching whether Team Romney or any of the other GOP contenders raise it during tonight’s debate.