Nuclear Summit Meeting Upstaged by U.S. Politics But this week, the American presidential campaign crashed into a nuclear security summit meeting half a world away. The result was a most undiplomatic pileup on Tuesday, with President Dmitri A. Medvedev of Russia criticizing Mitt Romney, the Republican presidential front-runner, for having views that were decades out of date, the White House siding with the Russians in knocking Mr. Romney, and the candidate in turn lashing out at both the White House and the Kremlin. The tempest began on Monday, when Mr. Obama was caught by a microphone in a moment of candor, telling Mr. Medvedev that he would have more flexibility to deal with Russian concerns over the American missile defense system after the election in November. Mr. Romney said such frank talk with a foreign leader was an "alarming and troubling development." The House speaker, John A. Boehner, said he would be curious to hear what Mr. Obama meant by "flexibility." On Tuesday, the president was with Mr. Medvedev again, this time to talk about a joint operation to clean up a nuclear testing site in Kazakhstan. Asked to clarify what he meant during his not-so-private exchange the day before, the president was primed to turn the tables. First of all, are the mics on? Mr. Obama said, gesturing to a forest of boom microphones. Then he plunged into a tutorial on the complexities of negotiating arms control treaties. In what sounded like the argument he has made against Republicans since the debt-ceiling debacle of last summer, Mr. Obama said the highly partisan environment in Washington would make it hard to bridge gaps with Russia on such sensitive issues. To do that, he said, the United States needs to win comparable cuts in the Russian arsenal, which required building trust - something it could do by resolving the disputes over missile defense. A few hours later, at a news conference, Mr. Medvedev joined the fray, saying that the attitude of some American presidential candidates toward Russia - especially Mr. Romney's characterization of Russia during a CNN interview on Monday as "without question our No. 1 geopolitical foe" - "smells of Hollywood." "Look at your watch," Mr. Medvedev told reporters. It is 2012, not the mid-1970s. No matter what party someone belongs to, he should pay attention to political realities. Jay Carney, the White House press secretary, sounded a similar theme in a briefing to reporters before Mr. Obama left Seoul to return to Washington. "In a world where Al Qaeda is so clearly the pre-eminent threat to the United States, and similar organizations, it seems a little inaccurate to make that statement about Russia, where Russia is a country that we have been able to cooperate with on very important issues," he said. White House officials said Mr. Romney's remarks were part of a pattern of statements about foreign policy issues, including on Iran and China, that left them shaking their heads. Mr. Romney's campaign kept the battle raging when it issued a letter to Mr. Obama, signed by 36 Romney foreign policy advisers, criticizing the president for leadership that "has been neither strong nor constant." His overheard conversation, the advisers wrote, raises questions about "whether a new period of even greater weakness and inconstancy would lie ahead if you are re-elected." Michael Schwirtz contributed reporting from Moscow, and Michael D. Shear from Washington.