I read that the President and his team regard the impeachment process as both a sham and unconstitutional, and for that reason only two of the thirteen subpoenaed to give evidence have bothered to comply. Yet, just as the identity of whistleblowers is protected by the law (but will the Department of Justice arrest Sebastian Gorka for revealing the whistleblower's identity, if true?), so an impeachment process is legal and constitutional.
it seems to me that the process taking place is designed to discredit the House of Represenatives and crucially, to detach it from the organisation of American government, and if the Senate rejects impeachment with McConnell and Graham insisting they won't even bother to read any of the testimony against their President, then Congress itself will no longer be a branch of government. The President, and any President, can do what he or she wants, and Congress can do nothing about it.
The choice is now simple: support the Constitutional separation of powers, or end it.