TAMPA, Fla. — This can’t be how the Romney campaign or rising Republican rock star Marco Rubio imagined it.

Moments before the freshman Senator from Florida took the stage to deliver the speech of his life — one that touched on a moving life story, conservative values and the American dream — 82-year-old actor Clint Eastwood was on stage here at the Tampa Bay Times Forum talking to an imaginary President Barack Obama and a real-life empty chair.

Despite a palpable discomfort in the arena, Rubio took the stage in a speech that many anticipated to be comparable to the keynote address delivered by a then-state Sen. Obama in 2004 that catapulted him to the presidency four years later.

Rubio, the son of Cuban immigrants, clearly rattled, began off-book “to ask for prayers” for “freedom and liberty” for Cuba. But then he took to the teleprompters and the rest could be history.

“A few years ago during a speech, I noticed a bartender behind a portable bar at the back of the ballroom. I remembered my father who had worked for many years as a banquet bartender. He was grateful for the work he had, but that’s not the life he wanted for us,” Rubio said, in one of the most emotive speeches of the shortened three-day convention. “He stood behind a bar in the back of the room all those years, so one day I could stand behind a podium in the front of a room.”

The forum erupted in cheers.

Rubio, who was on Romney’s short list for vice president, also delivered the most searing and impassioned indictment of Obama, gently conceding that while the president isn’t “a bad person,” he has not lived up to the lofty ambitions of his historic 2008 campaign.

“Hope and change has become divide and conquer,” Rubio said. “The new slogan for the president’s campaign is ‘Forward.’ A government that spends $1 trillion more than it takes in. An $800 billion stimulus that created more debt than jobs. A government intervention into health care paid for with higher taxes and cuts to Medicare. Scores of new rules and regulations. These ideas don’t move us ‘Forward,’ they take us ‘Backward.'”

What had begun in awkward silence, with confused delegates not understanding what was happening with Eastwood — billed earlier in the day as “a surprise guest” — had grown into excitement.

Rubio introduced Romney, and the crowd roared, but after a series of miscues, it’s unclear whether what could have been the story of the week will be able to rise above the gaffes that nearly squelched it.