Actually, to be fair to Trump, he does seem to be genuinely reluctant to go to war. My sense is that his strategy is to bluff (bully) his perceived adversaries & hope that that does the trick. This is an Art of the Deal type trick that may have limited success in the international arena with hard-boiled protagonists like NK, Iran & Russia. Combined with Trump's oddly fragile ego it could be very problematic, because when an adversary calls his bluff he either has to back down & seem weak, or go to war. Of course, the bald-faced lie also seems to have worked quite well for Trump.
I think you may be over-estimating the amount of opposition. True, there has typically been a very vocal minority opposing, say the Vietnam War, or the Iraq War, but they were always a minority, since "American Patriots" of all stripes always seem willing to rally around the flag, no matter who dubious the cause or justification.