I am going to push back a little.
The states could have charged him before he was elected
Why would any state have cause to investigate him? Being an ahole does not qualify. Being prominent news item does not qualify. Being "rich" does not qualify. There would have to have been justifiable reason to believe he broke a law.
They could be investigating and charging multitudes of wealthy people who are now, and always have, skirted the law because they are wealthy and can get away with it
Having an aggressive tax accountant does not qualify nor does being unethical.
Are there wealthly people who get away with literally "murder"? yep, but that does mean many or all wealthy folks do.
They could look into the finances of any corporation and likely find chargeable offenses
While in a world full of vulture capitalists one would or could derive the conclusion every corporation breaks laws to make money, I much rather suspect most try to remain within the lines for the simple reason they don't need to deal with the aggravation of legal proceedings.
And your fantasy of Trump in jail will go unfulfilled
Yep. I suspect even if he is indicted in some venue, he still has enough money to delay until he dies.
Impeachment will fail too
Yep. The Senate will not convict him even if he came to senate floor and shot Sen Shumer. Senate Republicans fear the Trump Base. A Base driven by bigotry and they have a bigot-in-chief occupying the WH. No Republican can withstand being primaried by these people.
More likel to get him re-elected than to hurt him
I suspect it would only make marginal difference and only among independents.
Our best bet is just to beat him in 2020
For the most part the people who are going to vote for Mr Trump are a fixed quantity. The national polls will have whomever runs against Mr Trump as winning, so the only feature to look at is state by state polling. What are battleground states doing ... you guys know the drill.
Look I think there are more than enough people who would vote for a stale ham sandwich rather than vote for Mr Trump. The problem will be to get those people to the polls in those critical states which will determine the electoral vote.
Vote ... vote often ... and vote for anyone but Mr Trump