Trump is back — and with him, the risk that the U.S. could unplug Europe from the digital world.

Donald Trump’s return to the White House is forcing Europe to reckon with a major digital vulnerability: The U.S. holds a kill switch over its internet.

As the U.S. administration raises the stakes in a geopolitical poker game that began when Trump started his trade war, Europeans are waking up to the fact that years of over-reliance on a handful of U.S. tech giants have given Washington a winning hand.

The fatal vulnerability is Europe’s near-total dependency on U.S. cloud providers.

Cloud computing is the lifeblood of the internet, powering everything from the emails we send and videos we stream to industrial data processing and government communications. Just three American behemoths — Amazon, Microsoft, and Google — hold more than two-thirds of the regional market, putting Europe’s online existence in the hands of firms cozying up to the U.S. president to fend off looming regulations and fines.