Analysis-U.S. rallies a united front against Russia as Putin seeks cracks

FILE PHOTO: U.S. President Joe Biden is seen through a window in the Oval Office as he speaks by phone with Ukraine's President Volodymyr Zelenskiy at the White House in Washington, U.S., December 9, 2021. REUTERS/Leah Millis/File Photo

WASHINGTON (Reuters) - A week of diplomacy by U.S. President Joe Biden failed to defuse tensions between Russia and Ukraine, but has maintained unity with European allies against Moscow as Russian President Vladimir Putin seeks to expose cracks, foreign policy analysts say.

After former U.S. President Donald Trump openly disparaged NATO and left Europe questioning Washington's commitment to the alliance, some analysts said Putin appeared to be testing Biden's declaration that "America is back" on the world stage.