Last week I criticized those conservatives who rushed to describe President Obama’s decision to withdraw a missile defense system from Eastern Europe as “appeasement.” The comparison to the appeasement of Hitler was simply absurd on its face. And, as I pointed out in a comment, the rationale for the move was unknown — how could conservatives even know if it was intended as appeasement?

Today, however, the picture has started to come into focus. The New York Times reports that Obama’s decision was part of a quid pro quo in which Russia agreed to support tougher sanctions against Iran:

President Obama, in his first visit to the opening of the United Nations General Assembly, made progress Wednesday on two key issues, wringing a concession from Russia to consider tough new sanctions against Iran and securing support from Moscow and Beijing for a Security Council resolution to curb nuclear weapons.

The successes came as Mr. Obama told leaders that the United States intended to begin a new era of engagement with the world, in a sweeping address to the General Assembly in which he sought to clearly delineate differences between himself and the administration of President George W. Bush.

One of the fruits of those differences — although White House officials were loath to acknowledge any quid pro quo publicly — emerged during Mr. Obama’s meeting on Wednesday afternoon with President Dmitri A. Medvedev of Russia, the first between the two since Mr. Obama decided to replace Mr. Bush’s missile defense program in Eastern Europe with a version less threatening to Moscow.

With a beaming Mr. Obama standing next to him, Mr. Medvedev signaled for the first time that Russia would be amenable to longstanding American requests to toughen sanctions against Iran significantly if, as expected, nuclear talks scheduled for next month failed to make progress.

“I told His Excellency Mr. President that we believe we need to help Iran to take a right decision,” Mr. Medvedev said, adding that “sanctions rarely lead to productive results, but in some cases, sanctions are inevitable.”

White House officials could barely hide their glee. “I couldn’t have said it any better myself,” a delighted Michael McFaul, Mr. Obama’s senior adviser for democracy and Russia, told reporters after the meeting. He insisted nonetheless that the administration had not tried to buy Russia’s cooperation with its decision to scrap the missile shield in Europe in favor of a reconfigured system.

Privately, several administration officials did acknowledge that missile defense might have had something to do with Moscow’s newfound verbal cooperation on the Iran sanctions issue.

I hope we can all agree that there’s a categorical difference between this sort of routine great powers diplomacy and giving land to Hitler so that he won’t invade other countries.