Finnish and Swedish leaders in Washington - but will Turkey sabotage the alliance's expansion?

President Biden - his ratings falling, Americans agitated and angry - has the chance to shake off the gloom today and play his favourite role.

He can project statesmanship when he hosts the Finnish president and the Swedish prime minister at the White House. Both nations want to join Nato, and they have the firm support of the Biden Administration and of Congress. Biden has called them "stalwart partners."

In fact, Biden will see their accession as something of a masterstroke, further punishing Russia and ensuring Moscow's war aims in Ukraine are a strategic failure.

Far from pushing Nato back to its pre-1989 borders, Russia will be facing a reinvigorated and expanded 32-member alliance, including a whole new front on its north-west borders.  If the aim is to ensure Putin's brutal invasion of Ukraine is a disaster, the accession of Finland and Sweden is the perfect prize for the West.

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But there is a problem.

For a country to join Nato, every member state must agree to it. 29 are giving Sweden and Finland the thumbs up. But not Turkey, the alliance's most recalcitrant member.

President Recep Tayyip Erdogan says that both Nordic nations harbour Kurdish militants from the PKK - as he puts it, Sweden and Finland are a "hatchery" for terrorist groups.

It is unlikely that Turkey will succeed in single-handedly stopping the Nato expansion. The pressure on Erdogan will be enormous. But he can name a price and use his veto as leverage.

If anyone knows how to drive a tough bargain, it is the authoritarian Erdogan.

So even as Sauli Niinisto of Finland and Magdalena Andersson of Norway arrive in Washington, their thoughts will be 5,000 miles away, figuring out how to bring Ankara on board.