• We need to to challenge regimes hostile to our interests and values;

What's wrong with standing up to those who are hostile to us?

The problem is : there are no countries or regime capable of challenging the US, since the end of the Cold War.
Any regime wanting to do so would be suicidal. BUT the US (or part of it) still believes it can be challenged, even though the US has a DOD budget almost as big as all the other countries' defense budgets united.

Then came 9/11....But that's the point: it wasn't a regime or a country, it was a group of terrorists united by ideology, religion, fanaticism and money from the oil. It wasn't a group of soldiers under the orders of a commander acting for a country, and that, I wonder if the US has understood it.
Terrorists have all the power in the world to change the rules of warfare if they want. They need to be stopped and using traditional military methods doesn't help. It makes the army and its country feel great and powerful but it definitely doesn't solve the problem.

I almost forgot North Korea: it loos like it indeed wants to challenge the US. But it looks that way and it hasn't so far and besides, talking to them helps ease the tension . That's often what a country or its dictator wants more than anything: international recognition by sounding threatening but only to catch the attention.
Using soft power is the best weapon.

Raoul