Agreed on the market angle and given the disconnect between SPX and the real economy a stock market focus is unlikely to pay big dividends (pun not intended) electorally! Deal collapse would be a big general risk-off trigger. Not least because the Phase One deal feels like a bit of a dam, holding back a more aggressive showdown - once it goes, all the other things which the national security apparatus want to apply follow quickly. Ironically it is the person who has set themselves up as the China hawk (ie Trump) that is - for the time being - holding back... the China hawks.
If the deal and market performance are intertwined on the way up, the danger is then presumably that if the market were to fall for some other reason - the rationale for keeping the deal intact is correspondingly weaker. Ie reflexive.