Updated

Now that President Barack Obama is back on U.S. soil, the criticism of his remark to the Russians about postelection flexibility on missile defense came fast and furious.

Republican Rep. John Boehner, who a day earlier said such complaints were inappropriate when the commander in chief is overseas, sent a letter to Obama on Wednesday saying he was alarmed by the remark and pressed the president for an explanation.

"I and other members of the House have previously expressed concern about your administration's apparent willingness to make unilateral concessions to Russia that undermine our missile defense capabilities," the Ohio Republican wrote. "Your comments reinforce those words."

Obama got caught on tape Monday telling Russian President Dmitry Medvedev that he would have more room to negotiate on missile defense after the November election. The gaffe forced him to explain his remarks on Tuesday. He said he did not have a hidden agenda with Russia and only meant that election-year politics make any nuclear arms reduction or missile defense negotiations extremely difficult.

In his letter, Boehner argued that Russia has backed Iran, Syria and North Korea, and questioned the wisdom of rewarding Moscow's "reckless ambition."

"That has significant implications for the security of our homeland, sends a terrible signal to our allies around the world and calls into question the effectiveness of your `reset' policy with the Russian government," Boehner wrote.

On Tuesday, Boehner sidestepped an opportunity to criticize Obama for telling Medvedev that he would have more flexibility, or to back Republican presidential hopeful Mitt Romney's remark that Russia is the U.S.' "number one geopolitical foe."

Asked if he agreed with Romney, Boehner told reporters, "While the president is overseas, I think it's appropriate that people not be critical of him or of our country. Clearly what's going on in Russia over the last couple of years raises some concerns."

Obama returned to Washington on Tuesday night. By Wednesday morning, Republicans and Independent Sen. Joe Lieberman, a former Democrat, were quick to respond when pressed on the president's comment.

"I thought that President Obama's statement to President Medvedev was disconcerting," Lieberman said at a news conference on Syria. "I don't know what the president meant when he said he'd be more flexible. I do think on the specific question on our missile defense in Europe, the president really ought to reassure all of us that he's going to stick with the program that we're on now because that program is, in my opinion, is critically important to the security of the American people for years and years to come."

Although Lieberman is one of two Senate independents who caucuses with the Democrats, he frequently has challenged the Obama administration on defense and foreign policy.

Republican Sen. John McCain, Obama's 2008 presidential rival, told reporters at the same news conference that the president was "playing fast and loose with national security."