"... to be confronted with the witnesses against him ..."

One of the more pathetic arguments I keep seeing among Republicans' attempts to pull Donald J. Trump's ass out of the crack he's got it in goes something like this (it's Ron Paul's site, trying to justify his son's Senate histrionics):

[Y]es, whistleblowers should have better protection whether government employees or contractors, but, he said, legislation and statutes cannot supersede the US Constitution, which gives everyone the right to face their accuser.

OK, so what does the Constitution actually say?

In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defence.

Emphases mine.

The obvious first problem with the Republican argument here is that an impeachment probe is not a criminal prosecution. It's the first, investigative stage of an employee disciplinary process. The maximum penalty here is that Trump gets fired, and that would only happen at a different, later stage involving upper management and, in some workplaces, the accused employee's union steward.

But sure, let's set that aside, frame impeachment as if it was a criminal prosecution, and see where that takes us.

Suppose a passerby notices three men, wearing ski masks and carrying Uzis, walking into a bank. The passerby dials 911 on a disposable phone, not publicly linked to her identity, to report a possible armed robbery.

The police respond.  Upon their arrival at the bank, they find three men, wearing ski masks and waving Uzis around, filling bags with cash while the bank employees and customers lie on the floor with their hands visible, quietly crying.

After a brief standoff, the suspects are taken into custody.

The matter is referred to a grand jury, which will decide whether or not to indict the suspects for armed robbery, etc.

The prosecutor plays the 911 call for the grand jury. He brings the responding police officers, the bank manager, the tellers, and several customers in to tell the grand jury what they know. He shows the grand jury security camera footage of the events, including footage of the suspects removing their ski masks and looking directly at the cameras after placing their Uzis on the floor. And so on and so forth.

At some point during this process, the suspects' attorneys object:

Unless the prosecutor publicly identifies the 911 caller and brings that caller in to testify, and releases the 9/11 caller's testimony to the public, they say, the suspects are being denied their right to be confronted with the witnesses against them.

Presumably the prosecutor would respond as follows:

1. The point at which defendants are entitled to be confronted with the witnesses against them is during the trial, if they are indicted. It's not a prosecution until and unless the grand jury tells the prosecutor "go forth and prosecute." Right now, it's a different thing entirely -- an investigation. It could conceivably end without ever becoming a prosecution.
2. It is, at this point, by no means obvious that the prosecution will use the 911 caller as a witness against the suspects at trial, if there even is a trial, and there's nothing requiring the prosecution to use the 911 caller in the grand jury process. The prosecution's case may start with the bank manager seeing the suspects enter the bank and pressing the bank's silent alarm button.
3. If there is a trial, the suspects will be entitled to compulsory process for obtaining witnesses in their favor, which means their attorneys will be able to compel the 911 caller to testify and be examined and cross-examined, if they believe the caller's testimony will benefit the suspects.

Sorry, Republicans: Even if impeachment was a criminal prosecution, there's just no constitutional "there" there for the claim that the prosecutor and the grand jury must talk to the "whistleblower" at all, let alone publicly.