One major danger to the "talking tough" approach is that, as someone pointed out, you can eventually talk yourself into a corner. Part of the argument for invading Iraq was along the lines of, "Well, we spent all this time building up for the war and our troops are already there."
Pulling back on the hammer, pointing the gun and then saying its a fait acompli is a pretty weak argument, but one that didn't get much criticism in the lead-up to Iraq.
The corollary to the cocked gun is the "we'll lose our credibility if we back off now" argument. How much more destructive is it to U.S. credibility than to invade and then have all of your pre-war arguments collapse in the light of day.