Guntram Wolff of Bruegel, a think-tank in Brussels, and Alex Burilkov of Leuphana University Lüneburg calculate the immediate requirement at 3.5% of GDP for Europe to be able to defend itself without the Americans—and in the longer term The Economist thinks expenditures will need to be more like 4-5%.

European defence stocks surged on Monday as governments faced pressure to hike military spending in the region, following calls from Washington for higher expenditure ahead of talks between the U.S. and Russia on a possible Ukraine peace deal.

The prime minister announced the UK will reallocate aid funds to boost military spending to 2.5% of GDP by 2027.

Europe would be "very vulnerable" without U.S. support, said Ed Arnold, a senior research fellow at Britain's Royal United Services Institute defense think tank.

Whether he is “beautiful” or not may be a matter of debate, but that the King is “very special” is surely no longer in any doubt. Both terms were used by President Donald Trump last week to describe Britain’s reigning monarch.

Europe after Trump This week European leaders have lined up to charm Donald Trump. But the broad smiles belie a bigger fear: what would it mean for the continent’s security if America forsakes its security