Afaict McMaster, while being the most hawkish of Trump's appointees until now, believed it was necessary to prepare for war with NK but still regarded it as a last resort. At least, that's the view most consistent with the way others who know him well describe him. Bolton, in contrast, sees pre-emptive war with both NK and Iran as Plan A. His appointment represents, I think, an increase in aggression and in the likelihood of wars--as well as an increase in the likelihood of those wars having more disastrous outcomes. Even if it turns out to be just for show.