U.S. relations with Russia face critical tests in 2014 as Putin, Obama fail to fulfill expectations

MOSCOW — With mutual trust all but gone, the United States and Russia enter a new year full of challenges that will test whether the world’s nuclear giants can salvage their relationship.

The Winter Olympics, the U.S. withdrawal from Afghanistan, the case of former National Security Agency contractor Edward Snowden, turmoil in Ukraine and Syria, and the uncharted consequences of the shale gas boom all threaten to bring new difficulties and irritants.