One of the arguments advanced for electing Joe Biden as US president was that he represented a safe pair of hands after the apparent chaos of the Trump years. That argument is now in tatters. First came the botched exit from Afghanistan and the return to power of the Taliban. Then followed a series of domestic set-backs: Mr Biden has not united Americans as he had promised but pursued a Left-wing agenda that has exacerbated divisions. Now, as Russian forces mass on the border with Ukraine, he faces perhaps his most serious test yet.

In a series of extraordinary remarks on the occasion of the first anniversary of his presidency, Mr Biden appeared to say that if Vladimir Putin made only a “minor incursion” into Ukraine then Russia would not face the devastating sanctions that had been threatened. What would count as a “minor incursion”? Some in Ukraine have accused Mr Biden of giving a green light to an invasion. His aides scrambled to clarify that any movement of Russian troops over the Ukrainian border would result in a severe US response.

Mr Biden also highlighted splits within Nato over how to respond to Russian aggression, at a time when a united front is surely most required. It is true that Western powers cannot seem to agree on how to deal with Mr Putin. The UK has flown anti-tank weapons to Kyiv, but avoided German airspace while doing so. Although it is said that no transit request was made, Germany is compromised by its dependence on Russian gas while it is switching off its nuclear power plants. Emmanuel Macron has been more robust, but talks in terms of a European strategic response separate to Nato. The French president has even suggested a European treaty with Moscow.

Suffice to say, this is a dangerous moment for the leading powers of the West to go wobbly. The UK alone appears to be firm in its resolve to help Ukraine resist Mr Putin’s forces, although there is no question of Britain playing an active role in Kyiv’s defence. It is possible that the Kremlin has no intention of launching a direct attack, but is instead playing a different game designed to extract concessions without war. Yet it would be grossly irresponsible to assume that is the case.

The urgent priority now is making clear to Mr Putin that he cannot do what he likes with another sovereign state without incurring overwhelming costs. Our allies are making that vital task harder.