Past military incursions by Mr Putin loom large as Mr Biden weighs his next steps.

In 2014, Russian troops marched into the Black Sea peninsula of Crimea and seized the territory from Ukraine. Russia’s annexation of Crimea was one of the darker moments for President Barack Obama on the international stage.

The US-Russia relationship was badly damaged near the end of President George W. Bush’s administration after Russia’s 2008 invasion of its neighbour Georgia after Georgian President Mikheil Saakashvili ordered his troops into the breakaway region of South Ossetia.

Rep. Adam Schiff, chairman of the House Intelligence Committee, said on Sunday that he feared that Mr Putin was intent on invading Ukraine and “nothing other than a level of sanctions that Russia has never seen will deter him”.

“Russia needs to understand we are united in this,” Mr Schiff told Face the Nation on CBS. “I also think that a powerful deterrent is the understanding that if they do invade, it is going to bring (Nato) closer to Russia, not push it further away.”