Mueller and his gang of democrat operatives have nothing on collusion so they want to set up a perjury trap for Trump.
If subpoenaed, Trump will go to the Supreme Court to fight it out. This will take many months.
If he loses, he will then plead the 5th.
It would be bad Public Relations and the media will have a field day but it’s what will have to happen. Anything Trump says the democrats will say he is lying and charge for perjury. So he will have to plead the 5th. Trump is not a precise speaker. He will probably have 100 counts of perjury charges after Mueller is done with him based on any minor misstatements.
Mueller is going to give congress a LONG laundry list of ‘crimes’ and ‘obstruction of justice’. It doesn’t matter if it’s not russia related. The media will go to defcon1, congress will impeach and depending on what is in the report(a legal fig leaf for the senate repukis), there will be enough repubikans to remove.