Russia-U.S. relations are at a post-Cold War low just about everywhere, except at the Iran nuclear talks.

Despite a chill over the Ukraine crisis that has spread to almost every element of their relationship, Moscow and Washington find common cause on a pressing issue on the global agenda — a deal to prevent Iran from being able to make nuclear weapons.

Officials credit each other with pragmatic proposals and good faith that transcends their broader differences.

For the U.S. and Russia, failure to get an agreement carries the unappealing risk of American involvement in a new Mideast conflict.

A former U.S. negotiator at the nuclear talks, Gary Samore, says getting an agreement is in Moscow's strategic interest as it tries to limit the U.S. presence in the Middle East.