In Denver today, former Republican presidential candidate and potential vice presidential pick Mitt Romney attacked presumptive Democratic presidential nominee Barack Obama, citing a lack of experience and judgment.

“Barack Obama is a charming and fine person, but he’s not ready to be president of the United States of America,” Romney said. “His experience does not provide for him the kind of judgment that is necessary to face the challenges” of being president.

Romney credited the Democrats’ vice presidential pick, Sen. Joseph Biden (D-Del.), with having foreign policy experience, but he added that it’s not the right kind.

“On the most important national security issue facing this country, which is Iran, Joe Biden has been wrong,” Romney said.

Romney termed the most important economic issue to be energy, particularly the nation’s dependency on foreign oil. He also mentioned immigration and health care.

“I’m afraid that the policies of Barack Obama would make America a weaker nation — weaker economically, weaker in terms of our national security,” he said.

At the same time, Romney reinforced the experience and record of presumptive Republican presidential nominee John McCain and said he was the right person to lead the country.

“You are never going to find someone say that John McCain [is] not qualified to be president of the United States,” Romney said.

Romney also emphasized what he called GOP unity, contrasting it to the nearly 50-50 split in the Democratic primaries between Obama and Sen. Hillary Rodham Clinton (D-N.Y.).

Alluding to his sometimes-testy exchanges with McCain during the GOP primary, Romney said that “Sen. McCain and I don’t agree on every issue, but on the major issues America faces, we agree.” These include not raising taxes, not curbing foreign trade agreements and expanding offshore drilling.

Romney sidestepped the question of whether he was in serious contention for the vice presidential slot.

“I trust Sen. John McCain’s judgment, in the same manner of which I do not trust Sen. Obama’s,” Romney said.