INTERNATIONAL: U.S. President Joe Biden has threatened to impose the harshest sanctions ever on Russia. He has worked to galvanize U.S. allies into a united front. He has supplied Ukraine with more weapons than any American president before him. And he has beefed up U.S. forces on NATO's eastern flank as reassurance of his commitment.

Despite U.S. President Joe Biden's efforts to head off a Russian attack against Ukraine, President Vladimir Putin was undeterred. On Thursday, he has authorized 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 have heard near Kyiv and in other parts of the country and Ukrainian President Volodymyr Zelenskiy has said Russia carried out missile strikes on infrastructure.

How the president of United States handles the crisis, which Western officials fear could spiral into the bloodiest European conflict since World War Two, is expected to have profound implications for his political fortunes and U.S. relations with the world.

Biden has vowed the United States and its allies would respond decisively to Russia's "unprovoked and unjustified attack."

But his handling of the biggest international crisis of his presidency has been deemed something of a mixed bag so far.

Biden was always going to be limited because his administration made clear it would do whatever it could to help Ukraine defend itself but was not going to put troops on the ground.

His preference for diplomacy and sanctions reflects the scant appetite Americans have for intervention after the Afghanistan and Iraq quagmires.

Putin had the advantage of knowing Biden was not going to war against another nuclear power to protect a country that shared a long border with Russia and with which Washington had no defense agreement.