But in the dead of night this week, Britain's military sent five tanks down the 30-mile "Chunnel" to test whether it would be an effective route for forces if deployed to places such as Eastern Europe amid tensions between Russia and NATO.

The fact that Wednesday's exercise came two days before President Trump's inauguration appears coincidental; the British army told NBC News the test had been planned for a year.

But the potential need to fast-track forces to the Russian front served as a reminder of how seriously Washington's allies in Europe perceive the threat on their doorstep. 

These allies have traditionally felt that Washington has their back, something thrown into doubt by Trump cozying up to Moscow and branding NATO "obsolete" earlier this week. 

German Foreign Minister Frank-Walter Steinmeier said these remarks caused "astonishment" and "agitation" across the continent, and NATO members are now facing a future where they may no longer be able to rely on Washington.