Iran's seizure and continued detention of a UK-flagged tanker deals Boris Johnson an immediate loyalty test: Britain's new prime minister may have to choose between Gulf escorts led by Europe or the United States.
Which way Johnson leans could set the tone for a complex agenda that includes withdrawing from the EU, striking a trade deal with the US, and maintaining or breaking European efforts to keep alive the deal curbing Iran's nuclear ambitions.
Some US commentators see this is a make-or-break moment for Europe's policy on Iran as a whole.
"Johnson could simply announce that the UK is joining America's maximum-pressure campaign and calls for a new (Iran nuclear) deal," the editorial board of The Wall Street Journal wrote.
"The rest of Europe would likely have no choice but to join its Anglophone partners -- and finally present a united front."
"But whether that is, in fact, how (Trump) will react I find it hard to say."
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