The New START treaty may only display the signatures of President Obama and Russian president Dmitry Medvedev, but its foreign-policy implications stretch far beyond the two nations. If Congress fails to ratify it, the most worrisome effect could be a cozier relationship between Russia and Iran.

As Republican senators, led by Arizona's Jon Kyl, voice doubts over ratifying the arms-reduction treaty during Congress's lame duck session, momentum for the treaty has stalled.

"This is a pivotal moment in not just U.S.-Russia relations, but also in Iranian-Russian relations. We don't want to upset the current trajectory of where things are going, and that's exactly what Sen. Kyl threatens to do," says Max Bergmann, a nuclear non-proliferation policy analyst at the Center for American Progress.

After the conflict between Russia and Georgia in 2008, when U.S.- Russian relations reached its worst point since the Cold War, the Obama administration has sought to improve that relationship, with the START treaty as an important piece of the puzzle.

With that progress has come less Russian support for Iran, a key to the administration's fight to strangle Iran in its quest for nuclear power.

This past spring, Russia supported the UN Security Council Resolution to impose strict sanctions on Iran. In September, Medvedev agreed to not fulfill a standing contract of selling advanced air defense--S-300 surface-to-air missiles--to Iran. The contract was suspended, but not terminated. "Russia [was] willing to forgo money in order to make Iran's nuclear weapons infrastructure more vulnerable to attack," explains Micah Zenko, a fellow for conflict prevention at the Council on Foreign Relations. Russia pursued a tougher policy toward Iran in part because of the "reset" in its relationship with the U.S. This was a stark contrast to its earlier funding of Iran's Bushehr nuclear reactor.

If the U.S. doesn't ratify New START, experts say it will prove to Russia that the U.S. can't deliver on its end of that "reset." Failing to ratify New START could mean a diminished incentive for Russia to formulate its Iran policy based on U.S. objectives, especially because Russia has both economic and geopolitical incentives for maintaining a positive relationship with Iran. Selling Iran weapons is lucrative, and positive ties with Iran means Russia has a geostrategic advantage in the region.

Even if it doesn't revive the surface-to-air missile contract, it could still back off on sanctions to Iran, and strengthen the Islamic Republic indirectly. Still, Russia doesn't want Iran to emerge as a nuclear weapons state. "In a lot of ways, in the last 15 years, [Russia] has tried to have it both ways," explains James Goldgeier, a professor of political science and international affairs at George Washington University. "They've tried to keep the relationship with Iran going without letting it get to the point where Iran would actually have a nuclear weapons program."

Obama and Secretary of State Hillary Clinton have tapped into that tension within Russia's Iran policy. For Russia, a benefit of prioritizing the prevention of an Iranian nuclear program was a stronger relationship with the United States.

But if failure to ratify the START treaty is seen as a betrayal of the "reset," or if we can't help Russia in some way,  then Russia loses the incentive to prioritize quashing Iran's nuclear program over maintaining positive ties with the country.

It appears unlikely that the Senate will ratify START before leaving town for winter recess.

Republican senators have said that they don't think there's enough time in the lame-duck session to vote on the treaty. Sen. Kyl cited the "complex and unresolved issues related to START and modernization." Tennessee Sen. Bob Corker's chief-of-staff, Todd Womack, told Foreign Policy's The Cable blog that Corker "believes it is far more appropriate to deal with major pieces of legislation like this in settings other than a lame duck session."

Sen. Richard Lugar, the ranking Republican on the Senate Foreign Relations committee, has accused the GOP senators of pushing back the START vote because they think "the lay of the land is going to be more favorable in January." Many analysts say the GOP is delaying the vote because they don't want to give Obama a perceived victory this year, even though the president called the New START treaty a "national security imperative."

Incoming GOP senators, meanwhile, who would vote on the treaty if its passage is delayed until January, see the New START agreement as an antiquated legacy of the Cold War. "They don't understand why we need an existing long term, sustained relationship with Russia," says CFR's Zenko. "They see the greater threat as coming from Iran and North Korea, and they don't see the connections."

If foreign-policy analysts are right, waiting to ratify New START could have more serious consequences than those Republicans expect.