You can plead the 5th all you want, that is obstruction without any executive privileges afforded such as Mulvaney, McGahn, etc., have. Pleading the 5th falls under obstruction and is a jail sentence until and in many cases the person does testify...
I believe that you should go back and revisit the 5th Amendment. To coerce testimony out of a person that would incriminate that person (such as charging them with obstruction for not testifying) would be a blatant violation of the 5th and the person(s) charging them would be subject to a Section 1983 violation which is punishable as a federal felony.
Like it or not, that's the way the Constitution is written and has been applied for the last 243 years.
Ed
