I don't think it matters whether congress investigates or not. Public trust in congress is down to 13%, those who think congress is honest is down to 10%. So who's going to believe their results unless their results are what one wants to believe? Minds are already made up way ahead of any potential investigation.
No need to go into the reasons why so many folks distrust congress or think they completely dishonest. everyone will have different opinions on that.
What will happen if congress does investigate, their report will be big news for a few days after they release it, the polls will probably spike in the Democrats favor. Then a couple of weeks later it will all be forgotten by the public as a whole, the numbers will return to the pre-release figures. It will be as if the investigation never took place.
The only congressional investigation that meant anything was the Watergate one, it resulted in the resignation of Nixon and huge gains in congress in the midterm elections of 1974. A gain of 49 house seats giving the Democrats 291 and 5 senate seats to 61.
I can't remember any high profile congressional investigations since that had any lasting effects. Not even Iran-contra. Shortly after that investigation, Bush I easily defeated Dukakis.
Most Americans have short memories and even a shorter attention span. I'm not saying having a investigation is the wrong thing to do, quite the contrary, it's the right thing. What I'm saying is 2 weeks to a month after, it'll be ancient history like it never happened to most Americans. Some other hot issue or major event will have taken its place. That's the way these things work.
Things taking place in the political arena usually have little lasting effect. Now the legal arena is different. This is why I say let the DOJ, the AG"s of New York and Atlanta continue their work. Their work will have a more lasting effect than any investigation which will be written off as a political side show. A partisan event which means nothing except for those of one party or the other.
Am I a cynic, you betcha. I became one way back in the 1990's.