Press conference by NATO Secretary General Jens Stoltenberg at the conclusion of the Brussels Summit,

[…] Moreover, the US presence in Europe is vital for the projection of US power to Africa, Asia and the Middle East.
To prevent turmoil there from reaching our shores.

And European forces, infrastructure and intelligence also help to protect the US, as we all face a more assertive Russia.

In short, NATO is a force multiplier for the US. Läs presskonferensen