A murdering mafia thug couldn't be charged for the folks he murdered. So they put him away for tax evasion. If collusion/conspiracy can't be proven can "they" be put away for money laundering or bank fraud or emoluments violations or treason or traitorship or other crimes? Get them out of the game. Anything they did wrong will do. It should be so easy because they did so many things wrong for so long and left lotsa tracks. Which track will prove most useful?