In forging a friendlier relationship with the Kremlin after years of tension, Mr Obama needs Congress to sign off on three major policy changes: an arms control treaty to reduce nuclear arsenals and resume inspections; a civilian nuclear agreement to permit greater co-operation; and a repeal of Cold War-era trade restrictions so Russia can join the World Trade Organisation.
Persuading Congress to approve any of those was already daunting when Democrats had control of both houses, but with Republicans taking over the House and bolstering forces in the Senate, all of these initiatives appear in jeopardy. If the president cannot deliver on his promises, American officials and foreign policy specialists fear it will rupture the so-called reset policy and validate Prime Minister Vladimir Putin and other hard-liners who have been sceptical of the rapprochement.
In the days since the election, Russian officials have already threatened to shelve the New Start arms control treaty. President Obama has decided to make a concerted push to persuade the departing Senate to approve the treaty in the "lame-duck" session this month.
If he fails to win approval before the old Senate adjourns, Mr Obama's advisers and allies worry that the relationship with Russia will be frozen at a time when they consider it critical to increase Russian cooperation on several fronts, most notably pressuring Iran to give up its nuclear programme.
Within the administration, a nightmare scenario envisions even worse consequences. Russian leaders traditionally have looked for weakness in American counterparts, and Mr Obama's failure to impose his will on Congress would be seen as a sign of impotence. That could undercut President Dmitri Medvedev, who has made the improved relationship between Russia and the United States a centrepiece of his tenure despite Mr Putin's doubts. If the reset comes undone, some analysts suggested it would hurt Mr Medvedev's chances of persuading Mr Putin to let him run for a second term in 2012. It could embolden those in the security establishment who want to keep close ties with Iran.
Sceptics of the New Start treaty say the administration overstates the chances that Russia would pull away if the pact is not approved during the lame-duck. "You see these reports that they're going to walk away from the treaty," said Stephen Rademaker, a former non-proliferation official in the Bush administration. "That's simply ludicrous. The treaty is totally in their interest.Their negotiators did a fantastic job of getting what they want."
Congress also has a say in two other central elements in Mr Obama's Russia policy. The president has revived a civilian nuclear co-operation agreement negotiated by former president George Bush. Under the law, Congress has 90 days to reject the agreement or it goes into effect.
The other Obama initiative has yet to be sent to Congress. To finally admit Russia into the World Trade Organization, the administration wants to lift an amendment to the trade act of 1974 that imposes restrictions on Moscow. Mr Obama's advisers worry that Republicans may use the issue as a proxy debate about Russia, essentially blocking Moscow's entry into the WTO.