Analysis: Putin's Ukraine assault puts Biden strategy to test

He threatened to impose the harshest sanctions ever on Russia. He worked to galvanise US allies into a united front. He supplied Ukraine with more weapons than any American president before him. And he beefed up US forces on NATO's eastern flank as reassurance of his commitment.

Despite US President Joe Biden's efforts to head off a Russian attack against Ukraine, President Vladimir Putin was undeterred. On Thursday, he authorised what he called a "special military operation" into the Donbass region of eastern Ukraine, marking a new high in post-Cold War tensions.

The scope of the offensive was not immediately clear. Explosions could be heard near Kyiv and in other parts of the country and Ukrainian President Volodymyr Zelenskiy said Russia carried out missile strikes on infrastructure.

How Biden handles the crisis, which Western officials fear could...