Rainier Ehrhardt / AP

From left, Nikki Haley, Mitt Romney and his wife Ann Romney, shake hands with supporters during a rally at Boiling Springs Fire Station on Friday in Greenville, S.C.

By NBC's Garrett Haake and Ali Weinberg
 
CHARLESTON, S.C.-- The lights were barely cool on Thursday night's debate stage in Sioux City when the news leaked out: South Carolina Gov. and Tea Party rising star Nikki Haley would be endorsing Mitt Romney Friday in South Carolina.
 
Add that news to a debate performance widely described as one of his better showings, and you get a presidential candidate having a very nice morning.
 
"Today I woke up with a big smile on my face,” Romney said Friday afternoon, still smiling. “I had fun in that debate last night."
 
With the endorsement in hand, and the final debate of the pre-primary season behind him, Romney was off and running on the start of an ambitious weekend swing through two states in which the former Massachusetts governor is looking to improve upon his 2008 results: Iowa and South Carolina.
 
Touching down in South Carolina, Romney was joined on stage by Haley for a boisterous rally at a Greenville firehouse. The fire marshal shut the door when the crowd hit 425 - a huge number for a Romney event - and dozens of attendees were left waiting outside.
 
Before the event began, the Romneys and Haleys stepped outside to shake their hands and to apologize for leaving them out in the grey drizzle. Inside, the mood belied the rainy day, with the candidate in high spirits as he took the stage.
 
“We’ve been hoping for this for a long, long time,” Romney said as he introduced his most important new surrogate in the first-in-the-South primary state.
 
“I can’t help it, but I’ve got to do this,” Haley said, leading the crowd in a rousing cheer to show their enthusiasm for the candidate in their midst.
 
Not an everyday event on the Romney campaign, where even the most enthusiastic crowds are generally restrained in vocalizing their approval.
 
The rally was indicative of the confidence of the Romney campaign, as it continued to flex it’s financial muscles Friday – debuting a new ad in New Hampshire, and the campaign’s first ad in South Carolina, where Romney is looking to best a disappointing third-place finish in 2008, and close a double-digit gap behind the frontrunner, former speaker of the House, Newt Gingrich.
 
“I want to win South Carolina,” Romney told reporters bluntly after the rally.

• SC governor endorses Romney

And while her poll numbers here in South Carolina have waned in recent months, Haley’s endorsement will no doubt help in that cause. She delivered a veiled rebuke of Gingrich when explaining her reasoning for choosing Romney.
 
“As we did the process of elimination, the one thing I knew we couldn't have was anybody associated to the chaos which is Washington, D.C.,” Haley said. “[Romney] is someone who has made decisions, real decisions, not just voted, but real decisions.”
 
That Haley ultimately endorsed Romney surprised few political observers here. The two have had a long political courtship. As a member of the South Carolina House of Representatives, Haley endorsed Romney for president in 2008, and served as a co-chair of his "Women for Mitt" team. When Haley ran for governor in 2010, Romney returned the favor; becoming her earliest major endorser, and contributing $62,000 to her campaign through various arms of his Free and Strong America PAC, according to the National Institute on Money in State Politics. 
 
Saturday, the two will campaign together at two town halls in the Palmetto state - in Charleston and Myrtle Beach.
 
Hawkeye on the prize
A morning town hall in a steel fabrication plant in Sioux City drew a small but friendly crowd for Romney, where he offered a speech heavy on personal anecdotes, and praised the newest Ryan/Wyden plan for Medicare reform as an important step in the right direction.
 
"I'm kind of proud," Romney said of the plan’s similarities to his own, calling it "good news" that Democrats and Republicans were working together on entitlement reform.
 
But it was an off-the-cuff remark about a different entitlement, Medicaid, that threatened to derail Romney Friday, as Democrats attacked the multimillionaire former-CEO as out of touch for saying he hadn't understood Medicaid until he got into government.
 
"You know I have to admit I didn’t know all the differences between these things before I got into government," Romney said while answering a question on entitlements. "And then I got into it and understood that Medicaid is the health care program for the poor, by and large."
 
As the DNC accused Romney of either indifference to the plight of the less fortunate, or of pandering, with that remark, Romney told reporters he meant the comment to be self-deprecating, and that his years working with health care companies and hospitals while a consultant with Bain taught him a great deal about Medicare and Medicaid. He said he learned the balance of the intricacies of the program as he ran for U.S. Senate in 1994.
 
Romney's campaign also released a statement calling the DNC attacks another example of "distortion and distraction" by Democrats looking to discredit Romney.
 
Back in South Carolina, Gov. Haley put a positive spin on those same attacks, calling it the “icing on the cake” that Democrats were attacking Romney, because, she said, it proved they were afraid to face him in a general election.
 
NBC's Andrew Rafferty contributed reporting to this story from Washington, D.C.