MANPADS are designed to be used against small CAS aircraft. Attacking large transport aircraft effectively requires a considerably larger air defense system. That also assumes you can move a MANPADS within range; the US already controls a large military airfield on Greenland.
Ok, and then what happens, Sun Tzu?
The end of the US as we know it happens. Sure the US could win a war ("win"), but the US without US Europe trade, EU turning to China as its main trading partner including in military equipment, no more bases in EU, less access to other parts of the world, and so on. That would be a US that would wither and die.