Aug. 28, 2012 -- Republicans celebrated the nomination of Mitt Romney as their presidential candidate tonight with funny hats and a determination to defeat President Obama, but their Tampa party was marred by a new poll that found Romney to be the least popular major-party nominee since 1984.

Tonight's nomination brought Romney into the home stretch of the long race to the White House and was a moment to be savored by the candidate and his party. Delegates danced in the aisles at the Tampa Bay Forum between speeches and cheered predictions that Romney was the next president of the United States.

But a new ABC News/Washington Post poll released this evening found that Romney has the lowest personal popularity of any major-party nominee in nearly 30 years.

More than half of all respondents, 51 percent, rate Romney "unfavorably," while only 40 percent rate him "favorably," a broader concept than simple likeability, which reflects a sense that the candidate understands the problems of average Americans, according to the poll.

No candidate has ever won the general election with such low favorability numbers.

By comparison, President Obama rates better but still not great. Fifty percent of respondents rate Obama "favorably" and 47 percent "unfavorable."

Romney survived a long and brutal primary, and well before becoming the party's official nominee tonight he has bore the brunt of attacks from President Obama, all of which have likely taken a toll on his ratings.

Inside the Tampa Bay Forum, isolated from news of the poll, the mood remained upbeat.

"How can you not be excited about this," New Jersey delegate Mike Donohue asked ABC News. "I was in Minnesota four years ago, it was nothing like this. Not that there wasn't enthusiasm, but it's off the charts this year, it really is."

But in an attempt to woo those outside the convention center, Republicans used the first night of prime time television coverage of the convention to reintroduce Romney to a broader swath of the American public, casting him as champion of family values and an economic reformer.

Headlining the primetime coverage of the Republican National Convention, Anne Romney and New Jersey Gov. Chris Christie – as different in disposition and they are united in their support of Romney – sought to energize the party faithful and swing independents as the race enters its final 70 days.

As she has done for more than a year on the stump, Ann Romney sought to humanize her often stiff husband, painting him as committed father of five boys and devoted husband who sustained her during life-threatening bouts of multiple sclerosis and cancer.

"I read somewhere that Mitt and I have a 'storybook marriage,'" Ann Romney said. "Well, in the storybooks I read, there were never long, long, rainy winter afternoons in a house with five boys screaming at once. And those storybooks never seemed to have chapters called MS or breast cancer," two diseases she has survived.

Ann Romney paralleled Romney's role as a family man to his ability to be president, pledging "This man will not let us down."

"I can't tell you what will happen over the next four years," she said. "But I can only stand here tonight, as a wife, a mother, a grandmother, an American, and make you this solemn commitment: This man will not fail. This man will not let us down."

Romney made his first appearance at the convention following Ann's speach, joing her briefly onstage for an embrace.

If Ann Romney's job was to make Romney more relatable and human, then it was Christie's to make him more presidential.

Much of the convention was built around a theme of "We Built It," a jibe against Obama whose remarks were construed to suggest that business owners were not responsible for their own success.

Many attendees wore hard hats or carried signs emblazoned with the "We Built It" motto.

Christie, the blunt talking governor of New Jersey, portrayed Romney as a business-minded reformer in his keynote address.

Romney, Christie said, would tell Americans the "hard truth we need to hear to put us back on the path to growth and create good-paying private-sector jobs again in America."

After a long and hard-fought primary season, Mitt Romney today officially became the Republican Party's presidential nominee, securing the 1,144 necessary votes. Delegates from New Jersey put Romney over the top, capping a race for the White House that began for Romney in 2004.

During a roll call in which each state pledged their delegates, Romney won the lion's share. However, each time delegates were pledged to Texas Rep. Ron Paul, the hall erupted in loud applause, indicative of his still insurgent support and fissures in the party.

Wisconsin Rep. Paul Ryan was later nominated to be Romney's running mate.

The roll call took place just hours after Romney arrived in Tampa today under sunny skies, a relief after Tropical Storm Isaac's threat postponed the convention for a day.

Isaac made landfall as a hurricane tonight along the Louisiana coast.