That's correct.
Jesus said very clearly that if one is struck on the cheek, that one should then turn the other cheek, to allow that also to be struck.
Jesus also made it quite clear that he did not intend to change the law in any way whatsoever. (Matthew 5:17.18) Thus, Jesus's word is not law, it's just a practical how-to guide on attaining salvation.
We are certainly not required to turn the other cheek. However, you'll find that it usually makes sense to consider your adversary's point of view before you get into a fight with him. Also, even if you disagree with his point of view, it pays to go out of your way to make sure you're not being unfair with him. After all, if you fight back, you've pretty much lost your chance ever to convince him and win him over to your side!
Yes, but it's pretty ridiculous to say that the United States was "founded" on "Christian principles" when the United States was founded on ARMED REBELLION!
We are certainly not required to turn the other cheek.
I guess that would depend on whether you consider yourself a Christian, and whether you, in your own words, follow Jesus':
..how-to guide on attaining salvation.