Highly contagious

The EU has raced to Spain's defence, after Donald Trump renewed his attack on Pedro Sánchez for what he sees as its lacklustre commitment to Nato. This confrontation fuses the two most contentious issues between Madrid and Washington - defence spending and tariffs. Despite agreeing on a wildly unfair trade deal with the US in August, Brussels has declared that any attempt by Trump to single Spain out for punishment will be dealt with "appropriately" - whatever that means.

Perhaps it's because I'm still recovering from a trip to London during last month's horrendous tube strike - but Trump reminds me of Eddie Dempsey, secretary general of the UK's Rail, Maritime and Transport (RMT) union. Both are bullish negotiators, willing to take hostages to get what they want. Neither is accustomed to facing resistance: Dempsey has a supine Transport for London (TfL) at his mercy, while Trump lords it over the EU.

EU Commission president Ursula von der Leyen effectively signed a note of surrender to Trump on his Scottish golf resort this summer, so it's a bit late for Brussels to talk tough. As well as agreeing to a blanket tariff of 15% on all goods exported to the US (three times higher than the previous average rate), the EU pledged to spend 750 billion US dollars on American energy and invest 600 billion in the US economy before the end of Trump's second term in 2028.

What did Brussels secure in return? Zero investment pledges from Washington and almost non-existent tariffs on most American goods coming into Europe. Though praised by the Italian and German leaders for preventing a trade war, the deal drew criticism across the bloc, including from Sánchez.

Brussels' attempt at bolshiness was further undermined by its assurance that this lopsided deal would provide the basis on which to "address any trade or trade-related issues". That's precisely why the US president will be chucking, rather than quaking, at its pledge to defend Spain. Nevertheless, there are limits to what even Trump can do by way of economic retaliation.

The EU's Common Commercial Policy (CCP) makes it impossible for individual member states to agree unilateral trade deals with third parties. To a certain extent, Spain is protected by this mechanism, even against a leader as capricious as Trump. The flipside is that the CCP drags the entire EU into localised trade standoffs.

Trump might not be able to lash out at Spain with even higher tariffs than those agreed on with Brussels in August. But he could vent his anger on the bloc instead, just as Dempsey takes the British capital hostage during TfL negotiations. Madrid's latest spat with Washington carries a high risk of contagion.