Fighter jets from the United States, France, Finland and Germany roar into the skies from a Dutch base as part of NATO's biggest air exercise this year.

The aim: to practice stopping -- and then defeating -- an enemy attack against the alliance as Russia's war in Ukraine fuels fears in Europe.

But while NATO focuses on the menace from the east, another potential threat is looming from within the alliance.

Since returning to office, US President Donald Trump has sowed doubt over Washington's commitment to underpinning European security and his administration has warned it could move forces away from the continent to deal with challenges elsewhere like China.

For now, NATO commanders insist nothing has changed -- showcased by the latest drills.

"We recently elected a new president, and we're still trying to figure out the exact policies that they're going to be coming out with," General James Hecker, the top US and NATO air commander in Europe, told reporters during the exercises.

"I think you're going to see us hand in hand with the Europeans for quite some time."

But if Trump does decide to withdraw US forces, there are fears that........

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