Being a former Navy vet having sailed throughout the waters in the Persian Gulf region - from Mediterranean Sea, the Suez Canel X2, the Adriatic Sea, the Straits of Hormez into the Persian Gulf X2 - I can tell you that the U.S. has had Navy warships in the region for decades ranging from an aircraft carrier battle group to smaller naval contingencies. All Iran is doing right now is postering, flexing their muscles so-to-speak. They've been itching for a fight with the U.S. for over 30 years. It's not surprising to see them do things just to egg us on.
Let Iran conduct their naval exercises. As long as they don't do anything stupid like fire upon one of our warships, there's really nothing to worry about. But if they do, we'd just unleash every cruise and/or Tomahawk missle we have on their butts and really turn Iran into a desert wasteland. But if all they do is institute a naval blockade of the Strait, I would hope that the President and all other U.N. member nations would join together to do whatever it took to stop the blockade including authorizing the use of military force. In other words, as long as we're not attacked I see no reason why the U.S. should take on Iran's threat of a blockade - assuming, of course, they carry through with the threat - by ourselves. It's international waters; the international community has a stack in this, too, probably moreso than we do since we import less OPEC oil now than we did 10 years ago.