For a second day, McCain criticized Obama for saying, in a debate last year, that as president he would meet with the leaders of Cuba, Iran and Venezuela without preconditions.
McCain insisted such a meeting could endanger national security, sounding a theme that is likely to persist until the November general election.
The Arizona senator recalled the ridicule President Carter faced in 1979 when he kissed Soviet leader Leonid Brezhnev during the signing of an arms treaty.
"Carter went over and kissed Brezhnev, remember?" McCain said Tuesday in Miami. "So it's dangerous; it's dangerous to American national security if you sit down and give respect and prestige to leaders of countries that are bent on your destruction or the destruction of other countries. I won't do it, my friends."
A woman in the audience applauded McCain's position: "For that, believe me, Florida will be yours," Ninoska Perez Castellon told McCain. She is a radio commentator for the anti-Castro station Radio Mambi.
A day earlier in Chicago, McCain raised the specter of a President Obama meeting with Iranian President Mahmoud Ahmedinejad. He said Obama displayed inexperience and reckless judgment in his willingness to talk with a sponsor of terrorism.
Yet while President Bush hinted last week that Obama wants to appease terrorists, McCain said he does not consider Obama or other Democrats to be appeasers. "I don't think they're appeasers; I think they have bad judgment," McCain told reporters Tuesday on his campaign bus.
Obama insisted the U.S. needs tough but direct diplomacy, like that employed by Presidents Kennedy and Reagan in negotiating with the Soviet Union in its day, and he blamed McCain and Bush for an Iraq war that he said has increased the threat from Iran.
An Obama adviser, Susan Rice, responded Monday on CNN that Obama didn't necessarily mean Ahmadinejad, although Obama himself has not disputed the assertion that he did.
On Tuesday, dozens of people at McCain's town-hall style forum booed as he raised the notion of a meeting with Castro, and they gave McCain a standing ovation when he said that, as president, he would pressure Castro to release political prisoners unconditionally, schedule internationally monitored elections, and legalize political parties, unions and free media.
McCain also criticized Obama for shifting his stance on the trade embargo against Cuba; Obama said in 2003 he would lift it but has hardened his position slightly to say he would ease it. McCain argues trade should not be normalized until the basic freedoms he outlined are granted.
Marking the Cuban independence day, May 20, McCain visited Miami's Little Havana, stopping at Casa del Preso, or the house of the prisoner, which helps unite Cuban political prisoners, and Versailles Restaurant, where an aide got him takeout Cuban sandwiches.
He expects to do well among Cubans and other Hispanic voters in Florida in part because of his support for a path to citizenship for illegal immigrants, although he says he has concluded the border must be secured before the government can resolve their citizenship.
McCain also criticized Obama for opposing a free trade deal with Columbia that could benefit Florida's agriculture and manufacturing industries. The pact, blocked by Congress, would eliminate high barriers facing American exports to Columbia. Most Colombian products already enter the U.S. duty-free.
In an interview with local reporters on his campaign bus, McCain said Obama "is a tool of organized labor ... He's been against (trade agreements with) Colombia, South Korea and several others. That's what labor unions want, no free trade agreements."
Later, McCain told his audience that blocking the trade deal won't create U.S. jobs, "but it will divide us from our Colombian partners at a time when they are battling the FARC terrorists and their allied drug cartels." He was referring to the leftist Revolutionary Armed Forces of Colombia.
Obama and Democratic rivalare scheduled to campaign Wednesday in Florida, underscoring the state's electoral importance.