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“I think it is nonsense, but during the past campaign it is a message that they drove home, and Marco Rubio drives through all those boundaries,” Mr. McDonnell said, advising the Miami native to explain to viewers in simple terms how the party’s free-market economic vision can help them.

“They are sitting in their living room, looking at the television, and they want to hear something from you that relates to them,” Mr. McDonnell said. “Marco Rubio is very good at that, and has a very good story about the American dream.”

Ana Navarro, Hispanic co-chairwoman of Mr. McCain’s 2008 presidential campaign, said Mr. Rubio has the ability to connect with young people and Hispanic voters — key slices of the electorate that helped propel Mr. Obama to a second term.

Marco did not get chosen because he is a token Hispanic,” Ms. Navarro said. “He got chosen because he is a good communicator; I think, the best orator in the Republican Party today. The fact that he is Hispanic and young is frosting on the cake. He embodies everything the Republican Party needs to attract.”

Mr. Rubio, like Mr. Obama, has risen to the peak of the GOP on the basis of oratory.

He introduced himself to conservatives at the 2010 Conservative Political Action Conference in Washington, wowing the audience with a keynote address about American exceptionalism and the sacrifices his parents made that “opened doors for their children that had been closed for them” in Cuba.

Later that year, he won his Senate seat, chasing the then-Gov. Charlie Crist from the GOP and easily winning the general election.

This past August, he broke onto the national stage with a well-received speech introducing Mitt Romney at the Republican National Convention in Tampa, Fla.

In tapping Mr. Rubio to deliver the official response, House Speaker John A. Boehner and Senate Minority Leader Mitch McConnell said they were counting on him to explain the GOP’s limited-government philosophy to voters.

But Mo Eliethee, a Democratic strategist, said the looming question is whether Mr. Rubio will offer new policy prescriptions that appeal to Hispanics, young voters and women.

“There are those that believe the Republican Party needs wholesale changes in terms of what it stands for and how it appeals to a large section of population,” he said. “Everyone agrees with that. The question is: Is it cosmetic or is it substantive?”