Mitt Romney officially clinched the GOP presidential nomination on Tuesday to move a step closer in his five-year quest for the White House.

To roaring cheers at the Republican National Convention in the packed Tampa Bay Times Forum, the delegation from New Jersey put Romney above the 1,144-delegate threshold, ensuring he will be the GOP challenger against President Barack Obama in November.

Earlier, the 2,200-plus convention delegates approved a conservative platform that called for less government, opposed same-sex marriage and endorsed a "human life amendment" to ban abortion with no specific exceptions for cases of rape, incest or when the mother's life is threatened.

Romney and his running mate, Rep. Paul Ryan of Wisconsin, will be formally nominated on Thursday, and Romney's acceptance speech that night will conclude the convention that had its agenda delayed by Hurricane Isaac.

With the storm churning toward landfall in Louisiana, Republican officials appeared determined to stick to a tightened three-day schedule that kicked into full gear on Tuesday with official business and speeches accusing Obama of failed leadership and undermining the American dream.

Republican National Committee Chairman Reince Priebus launched the litany of attacks, saying that another term for Obama and Vice President Joe Biden will mean "four more years of failure."

In reference to Obama, Priebus said "he hasn't even run a garage sale or seen the inside of a lemonade stand." The nation needs a president "with real experience in a real economy," Priebus added. "Mitt Romney will be that president."

Other speakers continued the effort by Priebus to frame the election as a referendum on the policies of Obama.

"The American people are still asking 'where are the jobs,' but President Obama only offers excuses instead of answers," said excerpts of planned remarks later Tuesday by House Speaker John Boehner. "His record is a shadow of his rhetoric. Yet he has the nerve to say that he's moving us forward, and the audacity to hope that we'll believe him."

Boehner also will say that "we can do better," adding that "it starts with throwing out the politician who doesn't get it, and electing a new president who does."

"President Romney will keep his word and his courage, too," say the excerpts from Boehner's speech. "He'll keep faith with the idea that government exists to serve the people, and the people build the economy."

Rep. Dan Benishek of Michigan complained earlier that Democrats in Washington were "spending away our children's and grandchildren's futures," while Rep. Tim Scott of South Carolina serenaded Obama with a chorus of the Ray Charles tune, "Hit the Road, Jack."

At a campaign event in Iowa, Obama said Tuesday that he expected the GOP convention to be "a pretty entertaining show."

"I am sure they will have some wonderful things to say about me," the president said. "But what you won't hear from them is a path forward that meets the challenges of our time."

Romney and his wife, Ann, flew into Tampa Tuesday morning and arrived at the downtown convention site two hours before the proceedings were scheduled to begin. Ann Romney is one of the featured speakers Tuesday night, with the keynote address to be given by New Jersey Gov. Chris Christie. Ryan and his family also arrived in Tampa early Tuesday afternoon.

Organizers acknowledged they were monitoring the hurricane, projected to make landfall in Louisiana as early as Tuesday evening, just a day before the seventh anniversary of devastating Hurricane Katrina hitting the state

Their concern is the perception of a celebratory convention atmosphere with colorful balloons and soaring rhetoric as a hurricane slams into the Gulf Coast, evoking memories of the havoc caused by Katrina and the ensuing criticism of the response of the Republican administration of George W. Bush.

However, Romney and Republicans are reluctant to lose any more of their best opportunity to define the candidate for the American people with less than three months until the election.

"He is a very shy guy. He is a humble guy. He doesn't like to talk about himself. That's who he is," Boehner said of Romney in an interview Tuesday with CNN. "But I've known Mitt Romney for a long time. Decent, honest, hardworking guy. And I think Thursday he'll have a chance to reintroduce himself to the American people."

The acceptance speech will give Romney a major chance to speak for himself, rather than be defined by either his Republican primary rivals or by Obama, Boehner said.

"He's been locked in this Republican primary and then locked into this battle with the president," the Ohio Republican added. "And as a result, people have all different kind of views of him. So I think Thursday night is clearly an important speech for him and I think he'll have a chance to reintroduce himself to the American people, most of whom are just paying attention now."

In a sign of lingering internal division in the party after a rugged primary campaign won by Romney, rival candidate Rep. Ron Paul of Texas was thronged by supporters when he entered the convention floor before Tuesday's session convened. Some Paul supporters shouted "let him speak," referring to their candidate's exclusion from the convention agenda.

Paul supporters later protested a rule change adopted by the convention that they believe will hinder their kind of grass-roots campaign in the future. They also cheered wildly when Paul received any delegates in the state-by-state roll call.

For Romney, 65, the nomination will put him closer to the goal he first sought in 2007 by running for president after serving as a Republican governor for four years in traditionally Democratic Massachusetts.

The multimillionaire businessman lost to veteran Sen. John McCain in the Republican primary campaign in 2008, then spent the next two years preparing for another try. He emerged victorious from the primaries during which rivals challenged his conservative credentials, and continues to walk a political tightrope that attempts to galvanize right-wing support while also trying to appeal to moderates and independent voters.