The president would have to rely on his “51st state” to track Chinese and Russian missiles that could come at the U.S. from over the horizon.

Canadian Prime Minister Mark Carney says his government is talking to the U.S. about joining President Donald Trump’s future Golden Dome missile defense program.

Some experts are worried about the cost and timeline of U.S. President Donald Trump's proposed Golden Dome missile defence system, which Canada has expressed interest in joining. They also say it could set off a space-based arms race that would escalate global tensions.