Because if he is not corrupt then the rest of our government is.
The best possible case for America is that Donald J trump is corrupt and guilty as charged.
IF, on the other hand , he is exonerated again we have a problem with the Obama Administration, The DOJ, FBI, CIA, DOD, State department, DNC, Democratic party, Pelosi, Schiff, Nadler and all the other democrats that have spoken against TRump.
IF trump is not guilty, they are guilty.
Best Case it is only Trump that is a crooked deviant. Worst case is that he is not and all the others are.