Boston (CNN) - Florida Sen. Marco Rubio would not be a wise pick for number two on the GOP ticket this year, former U.S. Attorney General Alberto Gonzales told CNN Saturday.
Rubio is not ready to be president, Gonzales said, and the vice president "must be ready on day one."
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"Rubio's resume does not reflect someone prepared to confront serious and dangerous issues that our country faces as president," Gonzales said.
Gonzales, who was the nation’s first Latino attorney general in the George W. Bush administration and remains one of the highest-ranking Latinos in U.S. history, questioned the staying power of the Florida senator's popularity with Latino voters.
Rubio might generate interest among Latinos "for the first 12 hours if selected for the number two spot, but that won't last," Gonzales said.
The Republican Party should do more to court Latinos, Gonzales said.
"We haven't seen the GOP reach out to Latino voters (in the primaries). We've seen them alienate that vote," he said.
Gonzales made the comments at a Harvard Latino Law, Policy and Business Conference and elaborated in a subsequent interview with CNN.
Elected in 2010, Rubio is frequently mentioned as a potential vice presidential pick for the presumptive GOP presidential nominee Mitt Romney.
He is a favorite among tea party voters, a charismatic speaker, a social and fiscal conservative and a senator from an electorate-rich battleground state.
It's believed putting Rubio on the ticket could help Romney make up ground among Latinos. A March Suffolk University poll shows Hispanics favor President Barack Obama over Romney 62% to 26%.
But Rubio has said more needs to be done to win over Latino voters.
"I'll tell you, the Hispanic vote has to be earned," Rubio said in an interview with CNN en Español Friday. "You can't just put somebody on there and say, 'This is gonna deliver it.' You've got to earn it, and primarily I think you earn it through economic policies."
The Florida senator Friday also reiterated his denial that he would be vice president.
"Marco has said repeatedly that he's not going to be vice president, and all of the speculation in the world isn't going to change that fact," said Todd Harris, a senior adviser to Rubio.
Rubio has said he would like the Republican Party to repair its image on immigration.
He recently suggested a Republican alternative to the DREAM Act, a stalled immigration bill that would give the children of illegal immigrants a path to citizenship.
Rubio's version would let the children earn non-immigrant visas that would allow them to stay in the United States without obtaining citizenship.
Some Latinos have criticized the plan, and a New York Times editorial described it as the "Dream Act without the Dream."
- CNN's Ismael Cala and Jim Acosta contributed to this report.