Peggy Noonan, who wrote brilliant speeches for Ronald Reagan and now writes gifted columns for The Wall Street Journal, and whose friendship I have enjoyed for many years, recently put forth a hypothetical historical analogy that stopped me in my tracks.

Let's look at some background before getting to it.

Late last week, the House of Representatives adopted a resolution authorizing formal investigations into whether President Donald Trump has committed impeachable offenses while in office. The resolution directed five House standing committees to investigate the president's behavior and to report the results of those investigations to the House Judiciary Committee.

Under House rules — enacted in January 2015, when Republicans had the majority — the Judiciary Committee has jurisdiction over impeachment, and it must air publicly the evidence it contends supports any articles of impeachment it may recommend to the full House.

The Constitution defines and limits the basis for impeachment as "Treason, Bribery, or other high Crimes and Misdemeanors." In Trump's case, it is "bribery or other high crimes" that have formed the basis of the impeachment inquiry.

Thus far, the House Permanent Select Committee on Intelligence has been holding closed-door hearings gathering evidence on these two points of constitutional inquiry. Why closed-door? No prosecutor or defense counsel would or ethically could offer a witness to testify publicly in a case without first having interviewed that witness in private.

These interviews are often open-ended, and the lawyer or investigator conducting the interview does not know in advance the full extent of what the witness can provide. Secrecy at this point enhances candor and permits an honest evaluation of the witness's credibility and usefulness to the case.

How did Congress acquire impeachment evidence in the past? In the cases of Presidents Richard Nixon and Bill Clinton, special prosecutors gathered evidence of presidential wrongdoing in secret and then presented that evidence to the House Judiciary Committee, which aired it publicly.

Today, even though the initial interviews of witnesses are taking place in secret, the Intelligence Committee is releasing transcripts of those interviews for the public to examine, well before it reports to the House Judiciary Committee.

We know from those transcripts that Trump's threat to hold up $391 million in military hardware and financial aid to our ally Ukraine — which is fighting a bloody war with Russia — until the Ukraine government gave him a "favor" by commencing an investigation of former Vice President Joe Biden and his son Hunter, was not a one-off.