BRUSSELS, April 2 --  "Paper tiger". "Cowards". As US President Donald Trump grapples with the fallout of his war on Iran, much of his anger has been redirected onto another target: the Nato military alliance.

Enraged by European allies who have refused to back his fight, rejected demands to help reopen the Strait of Hormuz, or denied access to US jets, Trump's tone has grown increasingly menacing.

"I was never swayed by Nato. I always knew they were a paper tiger," Trump told British newspaper The Telegraph Wednesday, suggesting he was strongly considering pulling the United States out.

The ire from the president - who has also blasted Nato allies as "cowards" over Iran - is just the latest existential crisis to grip the 77-year-...