I think the term "Constitutional crisis" is nearly as misused as "Treason" these days.  We haven't seen either in recent history, IMO.  

Uncertainty on lots of levels are bad for equities, since one of their functions is to factor/price risk and uncertainty in the future of US leadership certainly can make the markets nervous.  That being said,  I think the Mueller "investigation" has been largely priced in and I don't think the markets are overly concerned.

Current driving factors, IMO,  are the fed, convincingly demonstrated after the overreaction to Powell's perceived Dovish comments on Wednesday.  And the trade war(s),  which is the primary focus today. Neutral to positive out of the G20 between Trump and Xi will have a very positive effect in the coming week(s). Negative, or escalation of tensions, will have a very negative effect.  

As Trump prides himself on not letting anyone know what he is up to till after the fact,  we can't be sure.  I believe he remains in the drivers seat on this.  Xi is a significant co-pilot,  but Trump will determine what is taken away from the upcoming meeting/confrontation.

I suspect we'll end up somewhere around neutral. 

I did say that a constitutional crisis was not likely, just a possibility.  Perhaps there is a better word/phrase to use.  Was it a constitutional crisis when Nixon went head to head with congress and then the Supreme court?  No, because he stepped down.  Similarly with Clinton.  Things blew over.  But the system was tested.  I'll let you pick a better word/phrase.  The markets did get hit.  

The latest on the Muller front is that yesterday Trump admits he was doing business with the Russians and said "what is wrong with that?"  No law broken perhaps, but a direct contradiction with his previous claims that he had "no business with Russia".  A defense attorney's nightmare is a client who tells him/her 70% of the truth.

I agree with you on the Fed and interest rates.  But on trade (or trade war) I'll differ slightly.  If we make some real progress at the G20, such as a joint statement that negotiations will resume and a set date on resumption, I think the market gets a nice 1-2 day rally.  But I would sell that rally.  Mainly because I think both sides in the end are going to be stubborn.  Hard to know for sure with Trump.  On the one hand he really believes in this fight and has for many years.  On the other hand he might make a weak deal (declaring it a strong deal) like he did with N. Korea.  But even a weak deal would be bullish for more than a 1-2 day rally.  But I think a protracted standoff is the most likely scenario.   China might get hurt more by a trade war, but it would be bearish globally for the economy and stocks in general.  If the world gets the flu, we are sure to at least get a cold.