Frankly, if Medvedev truly favors Obama -- as he'd be rational to do, given the President's apparent amenability to concessions after he's reelected -- he'd probably help him more by staying silent. The American people realize that Medvedev and Putin are not champions of American interests, but of their own. To the extent they favor one American candidate over another, that signals they believe their favored candidate, President Obama, will be weaker in his dealings with them.
Indeed, President Obama's whispered promises to Medvedev are chilling because they signal clear duplicity in his dealings with the people he's sworn to represent. What's almost equally chilling is that he apparently feels more comfortable being frank about his intentions with a foreign leader than he does with his own countrymen.