This is a very good presentation, perhaps reiteration is a better word, of the nature and process of impeachment in the US as it now exists. It is a carefully worded but very clear admission of system failure.
The key statement indicating this is that the system was designed for the three divisions of government to work in conjunction and, at least, minimal cooperation to achieve common national goals. Because the impeachment process is strictly a political process it must assume a shared belief in the integrity of all involved. Failure to maintain that integrity by an official is the actual reason for impeachment.
As shown in this article that process must be able to rise above the normal partisan power goals. It did in the forced resignation of Nixon. It is failing completely in the face of a complete absence of integrity on the part of the person in the presidency and in the actions of those who are using that person as a tool to achieve autocratic power.
Without going into the detail of the late 18th century and the revolution against divine right monarchy, the founding assumption that establishing power in the people would constrain the people’s representatives from falling completely under the influence of someone who was unable to understand or to support representational government. It’s very hard to establish a system of self regulation and removal of such people from authority if the base assumption of integrity and political ideals are disregarded.
Yet, that is the situation now. While this is built on contested and partisan debate as the means of government that has collapsed. This has been dealt with in the past by maintaining, at least, the pretense of shared representational government as the overall ideal. Nixon was caught out by lying about trying to cover up his actions. He maintained his innocence until the end by claiming his commitment to the shared ideal. That having been proved a lie was the end as that pretense cannot be allowed to lapse.
There is no longer even a pretense under the Trump administration and the current Republican leadership in Congress of any shared ideal. These things have been publicly denounced and their very validity denied. All actions to date have confirmed that there is no assumption of anything but direct power for personal gain.
Even though there are diverse actions that call for impeachment there is no moral or ethical standard that applies. The weak impeachment process was based solely on shared standards and/or willingness to accept national law as the standard. That has also been openly denied. No law applies.
Trump can do what he wants as there is no need for integrity, honesty, or any shared standard. No process remains that can limit executive action criminal or otherwise. This is autocracy and there is no existing means of action.
The Constitutional system has failed. Whether Nancy Pelosi can or should begin impeachment is a moot point. She has no viable institutional process to use.