Trump doesn’t lose support of congresspeople except those on their way out. I don’t suspect nukes would change that equation, despite wreaking havoc on markets and humanity as a whole. The right wing propaganda machine would find an angle (probably fear of imminent attack) to make it seem prudent and even heroic. The reins have been shredded for a long time and the horse just keeps running wild, cheered on by those who would have any power to wrangle it.