SAN DIEGO – Republican presidential front-runner Mitt Romney on Monday called President Obama’s open-mike comments to Russian President Dmitry Medvedev “an alarming and troubling development.”

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 At a campaign stop here, Romney lashed out at Obama for telling Medvedev that he would have more “flexibility” to continue bilateral talks between the United States and Russia over missile defense after his fall reelection campaign.

Obama had told Medvedev during what he believed to be a private conversation, “On all these issues, but particularly missile defense, this, this can be solved but it’s important for him to give me space.” Obama appeared to be referring to Russian Prime Minister Vladimir Putin.

Medvedev had replied that he understood, to which Obama interjected, “This is my last election. After my election, I have more flexibility.”

Unbeknownst to both leaders, their chat had been picked up by an open microphone.

“When the president of the United States is speaking with the leader of Russia, saying he can be more flexible after the election, that is an alarming and troubling development,” Romney said. “This is no time for our president to be pulling his punches with the American people – and not telling us what he’s intending to do with regards to our missile defense system, with regards to our military might and with regards to our commitment to Israel and with regard to our absolute conviction that Iran must have a nuclear weapon.”

A campaign spokeswoman said Romney misspoke and intended to say that Iran must not have a nuclear weapon.

Romney effectively attacked Obama for the same kind of political flexibility that his own senior adviser, Eric Fehrnstrom, seemed to be referring to last week when he likened Romney's restart of his campaign in a general election to an Etch A Sketch toy.

The missile defense issue has been a longstanding source of tension in the U.S.-Russia relationship.

In December 2010, during the lame-duck session of the 111th Congress, the Senate ratified the new START Treaty, a comprehensive U.S.-Russia pact calling for a reduction of up to 30 percent in deployed long-range warheads in both countries.

Obama has hailed that treaty and is aiming for further bilateral cuts, but those plans could be scuttled by Russian opposition to a planned NATO missile defense shield. Moscow argues that it has received insufficient assurances that the anti-missile shield would not be wielded against Russia.

In both the 2010 new START ratification and the latest missile defense debate, domestic political considerations have played a large role. Senate Republicans, many of whom had expressed reservations about the deal, had contended in the START debate two years ago that the treaty was being “rammed through during the lame duck session” when Democrats held a wider majority in the chamber than they do now.