TAMPA, Florida — Mitt Romney will tout a "more positive vision for America" on Thursday when he accepts the Republican Party's White House nomination, a senior aide said.

"It will be a clear vision of a Romney presidency, and very much from his heart about America, and why he wants to be president," strategist Stuart Stevens told reporters Tuesday aboard the Romney campaign plane.

Romney flew to Tampa with his wife Ann, who was to take the stage Tuesday after delegates officially bless the Republican flag-bearer as their champion to challenge President Barack Obama in the November 6 election.

Both campaigns unleashed a barrage of attack ads against the other in the early stages of the race, leaving both with lower approval ratings and exposing them to criticism over the negative tone.

Pundits now see the Republican National Convention in Tampa as Romney's chance to set out his own stall rather than insulting the incumbent.

The three-day event -- shrunken from four days due to the threat of Tropical Storm Isaac on Monday -- reaches a crescendo with Romney's acceptance speech, and Stevens said the candidate had finished writing his remarks.

"He always likes to change things up until the last minute, but yeah it's finished," said Stevens, who hunkered down with the Romneys for two days of speech prep before heading to Tampa.

He stressed that Romney, who launched his presidential campaign from a New Hampshire farm more than a year ago, will be returning to "the arguments and themes that he laid out when he first announced for president."

But Romney will also sell "a different, more positive vision for America" than that of the stubbornly high unemployment and "economic stagnation" that he said says marked the three-and-a-half years of the Obama administration.

"This excitement that people felt when the president took office really hasn't been fulfilled," Stevens said.

The question Romney will be asking, Stevens said, is "do we accept that disappointment, or do we think that we can do better? And that's really what this race is going to be about."

Stevens, a long-time Romney confidante, said it was "extraordinary that we're going into the convention tied or with the lead," given that Obama's machine has spent what he estimated at half-a-billion dollars on the race.

"If the election were held tomorrow, we'd win, and win pretty easily," he said, citing polls that show Romney even with Obama or slightly ahead. Most polls still give Obama a slight advantage, especially in key swing states.

Stevens said Romney has been thinking about his address for months, poring over others' acceptance speeches, as he seeks the right combination of positive inspiration and Obama criticism.

"These are really his words, his ideas, his policies, what he wants to tell the country about his plan for moving the country forward," advisor Kevin Madden said.

Foreign policy will be featured in the speech, but when asked if Romney would address the war in Afghanistan, Stevens would not be drawn on specifics.

He said Romney is also set to talk about Isaac, which slapped Florida on Monday prompting a one-day delay to the convention, but which is now bearing down on New Orleans as a fully-fledged hurricane.