As much as I think Sen. Menendez probably was involved in some criminal and unethical activity connected to his office of public trust, he still is entitled to the unique due process procedure adopted into our Constitution for one holding a federal office of public trust who violates that trust. And that procedure requires the House to impeach and the Senate to convict, before he can be made
“… liable and subject to Indictment, Trial, Judgment and Punishment, according to Law”, as per Article I; Section 3, Clause, 7:
”Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law."
Your problem is that this clause doesn't say that impeachment
must precede a criminal trial. It simply says that if a party is removed from office via impeachment he can still be held accountable for any alleged criminal activity. Such a result should be obvious, since impeachment is a civil matter and not a criminal one and that removal from office needn't be based on any criminal activity (one federal judge was removed for drunkenness, which by itself isn't a crime).*
The Nixon case is inconsistent with your theory that impeachment must precede a criminal trial. I guess Nixon, his lawyers, and the judge all missed your theory. Not surprising, since there's nothing in the Constitution to support it.
George Carlin explained this in his brilliant discussion of everyday expressions:
