SEOUL, South Korea (AP) -- President Barack Obama told Russia's leader Monday that he would have more flexibility after the November election to deal with the contentious issue of missile defense, a candid assessment of political reality that was picked up by a microphone without either leader apparently knowing.
Obama's Republican opponents pounced on the comment, saying the president has a hidden agenda that could include concessions to the Russians if he is re-elected this fall.
"This is my last election," Obama is heard telling outgoing Russian President Dmitry Medvedev. "After my election, I have more flexibility."
Medvedev replied in English, according to a tape by ABC News: "I understand. I will transmit this information to Vladimir," an apparent reference to incoming President Vladmir Putin.
Obama and Medvedev did not intend for their comments, made during a meeting in Seoul, South Korea, to be made public.
Once they were, the White House said Obama's words reflected the reality that domestic political concerns in both the U.S. and Russia this year would make it difficult to fully address their long-standing differences over the contentious issue of missile defense. Obama, should he win re-election, would not have to face voters again.
"Since 2012 is an election year in both countries, with an election and leadership transition in Russia and an election in the United States, it is clearly not a year in which we are going to achieve a breakthrough," White House deputy national security adviser Ben Rhodes said.
Obama's candid remarks Monday illustrated the political constraints that hem in any president who is running for re-election and dealing with a congressional chamber -- in this case, the House -- controlled by the rival party. Republicans have fought Obama fiercely on health care, taxes and other issues. They are eager to deny him any political victories in a season in which they feel the White House is within reach, although Obama's remarks suggested he feels good about his re-election prospects.
Even if Obama was confiding a political reality in a supposedly private moment, the comments gave the GOP new openings to question his sincerity and long-range plans.
Mitt Romney, the leading Republican contender to face Obama this fall, told a San Diego audience the unguarded comments were "an alarming and troubling development."
"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," Romney said.
Romney, a former Massachusetts governor who often faces charges of having been flexible on his own policies over the years, also issued a statement saying Obama "needs to level with the American public about his real agenda."
Obama campaign spokesman Ben LaBolt said Romney "is undermining his credibility by distorting the president's words."
Republican presidential candidate Newt Gingrich also questioned Obama's motives.
"I'm curious, how many other countries has the president promised that he'd have a lot more flexibility the morning he doesn't have to answer to the American people?" Gingrich said on CNN.
Rep. Mike Turner of Ohio, Republican chairman of the House Armed Services Subcommittee on Strategic Forces, wrote to the president requesting an "urgent explanation of (his) comments." Turner said Congress "has made exquisitely clear to your administration and to other nations that it will block all attempts to weaken U.S. missile defenses."
The Republicans' sharp remarks underscore increased willingness of politicians to criticize a president on a foreign trip. The old adage "politics ends at the water's edge" is a casualty of the nation's heightened partisanship in recent decades.
Tensions over missile defense have threatened to upend the overall thawing of relations between the U.S. and Russia in recent years.
Both leaders acknowledged as much in their public statements to reporters following their meeting. Obama said there was "more work to do" to bridge their differences. Medvedev said each country had its own position on missile defense but there was still time to find a solution.
Congress, as part of the fiscal 2012 defense authorization act, constrained Obama's ability to share classified U.S. missile defense information with Russia. Obama signed that legislation into law.
Russia has strongly criticized plans for a U.S.-led NATO missile defense in Europe. Russian officials believe the planned missile shield would target Russia's nuclear deterrent and undermine global stability. The U.S. says the planned missile shield is intended to counter threats from Iran.
Putin said earlier this month that Washington's refusal to offer Moscow written guarantees that its missile defense system would not be aimed against Russia deepened its concerns. Putin won elections earlier this year and will return to the presidency later this spring. He is expected to name Medvedev prime minister.
The United States and Russia have also clashed recently over their approach to dealing with violence in Syria. The U.S. has sharply criticized Russia for opposing U.N. Security Council action calling on Syria's president to leave power.
Obama said Monday that despite past differences on Syria, he and Medvedev agreed they both support U.N. envoy Kofi Annan's efforts to end the violence in Syria and move the country toward a "legitimate" government.
Associated Press writers Kasie Hunt in San Diego and Donna Cassata in Washington contributed to this report. Babington reported from Washington.