Earlier quoted context omitted.
Presidents being impeached (and their administrations) have always refused Congress's requests for testimony and documentation. Congress can take the President to court and compel documents and testimony (or else face contempt of court and imprisonment like Manning). The House did exactly that for Nixon and Cliton. For Trump, the House chose not to do that, because (I believe) it would slow them down, and that wasn't…
How was Clinton testifying also him refusing to testify? Your claims differ from history.
The ratified Articles of Impeachment were in fact (1) Perjury and (2) Obstruction of Justice (witness/evidence tampering).
I may have mistakenly characterized Clinton as explicitly withholding information by invoking executive privilege like Nixon and Trump, rather than deceptively doing so.
https://en.wikipedia.org/wiki/Impeachment_of_Bill_Clinton#Ar...