It depends on the US objectives. Europe has no way to attack the US across miles of ocean covered by 12 carrier battle groups, around 30 688i SSNs, something like 500 F-15s and 2000 F-16s.

Europe has a shitty French carrier and 2 British Harrier-carriers (somehow I think the British would side with the US)
the US has 12 fleet carriers and 12 LHAs (double as Harrier-carrier) plus dozens of Aegis cruisers and destroyers. Aegis, being designed to counter Soviet "Granit" (NATO SS-N-20 Shipwreck) anti-ship missiles, can shoot down anything anyone can throw at it biggrin:

A land invasion would be more difficult, but the US could easily blockade water shipping routes to Europe.