Paul Begala, a Democratic strategist and CNN political commentator, was a political consultant for Bill Clinton's presidential campaign in 1992 and served as a counselor to Clinton in the White House. The opinions expressed in this commentary are his. View more opinion articles on CNN.

(CNN) As the House debated impeaching the President of the United States, before eventually voting to do so on both articles, I read and reread the six-page screed Donald Trump sent to House Speaker Nancy Pelosi on Tuesday decrying his impending impeachment. Having helped defend a President against impeachment, I know something about the issue. I have read -- and written -- countless pages on the topic, from Alexander Hamilton to Andrew Johnson.

But I've never read anything like this.

So I read it again. Doing so has helped me see Mr. Trump more clearly. It made it harder to watch the debate, though, as I saw good people -- and many of the House Republicans are indeed good people -- kowtow to this malignant, malevolent man.

Trump's letter to Pelosi has been described in clinical terms. It has been called " deranged " or just plain " sick ." But while I appreciate the need to understand Trump, I do not believe that understanding will be found in psychology.

There are a variety of reasons for this. First, I never even took freshman psych in college, so I am utterly unqualified to render psychological evaluations. Second, it is ethically dubious for trained professionals to diagnose public figures they've never met. Third, I do not want to stigmatize mental illness. Millions of people struggle with various forms of mental illness. Few of them behave as cruelly and criminally as Mr. Trump.

But most important, excusing Trump as merely ill lets him off the hook too easily. So, rather than leaning on psychiatry, I think we ought to dig deeper for a more meaningful, powerful, and accurate nomenclature. His letter is not sick; it is evil. His conduct is not deranged; it's tyrannical. I hope every member of Congress reads it.

In my multiple readings, one sentence, however, struck me more than the others. Perhaps because it's one of the few that I think is 100 percent honest: "I write this letter to you," Mr. Trump says in the penultimate paragraph, "for the purpose of history and to put my thoughts on a permanent and indelible record." This is Trump speaking to history. This is his manifesto.

And his manifesto, of course, is shot through with lies , mendacity being Trump's native tongue. Like many people, Trump lies when it suits his purpose, but his assault on the truth, particularly in this letter, is essential to his mode of governing. Killing truth is not merely a means to an end for Trump; it is a vital end in itself.

Autocrats must attack the truth, because, once unmoored from facts, followers have no choice but to accept what the Dear Leader tells them. "In the end," George Orwell wrote in 1984, "the Party would announce that two and two made five, and you would have to believe it. It was inevitable that they should make that claim sooner or later: the logic of their position demanded it. Not merely the validity of experience, but the very existence of external reality was tacitly denied by their philosophy."

In 2019, Trump has reconstituted 2+2=5 as "I had a totally innocent conversation with the President of Ukraine." A " perfect conversation ," even. Two plus two make five, echo the House Republicans. One after another, they wait in line on the House floor to bark their obeisance to Trump's falsehoods -- or, to use the White House's term, " alternative facts ."

Trump's next battle is against anyone who has fidelity to the truth -- especially when the truth does not serve his agenda. He meets all checks and balances, all restraints on his power, with fire and fury. "The Articles of Impeachment," Trump writes, "are not recognizable under any standard of Constitutional theory, interpretation or jurisprudence."

Any standard? Really? The 1,500 and counting historians, law professors and constitutional scholars who have signed onto a letter calling on the House to impeach Trump disagree. They say these articles of impeachment clearly meet the standards set by the Founding Fathers.

"Collectively, the President's offenses, including his dereliction in protecting the integrity of the 2020 election from Russian disinformation and renewed interference, arouse once again the Framers' most profound fears that powerful members of government would become, in Hamilton's words, 'the mercenary instruments of foreign corruption.' It is our considered judgment," they conclude, "that if President Trump's misconduct does not rise to the level of impeachment, then virtually nothing does."

The Democratic-controlled House itself is illegitimate, in Trump's eyes. "By proceeding with your invalid impeachment," Trump wrote the speaker, "you are violating your oaths of office, you are breaking your allegiance to the Constitution, and you are declaring open war on American Democracy."

And that was him only getting warmed up. "You dare to invoke the Founding Fathers in pursuit of this election-nullification scheme -- yet your spiteful actions display unfettered contempt for America's founding and your egregious conduct threatens to destroy that which our Founders pledged their very lives to build."

This of course, is not new from Trump.

His letter mirrored what he told Guatemalan President Jimmy Morales in a meeting Tuesday when he unloaded on House Intelligence Committee Chairman Adam Schiff, saying, "In Guatemala, they handle things much more diff -- much tougher than that." Trump appeared to be referencing Guatemala's tragic history of political violence: From 1960 to 1996, some 200,000 people were killed or disappeared.

Yet when Trump unsubtly threatened violence against members of Congress, not a single Republican member of Congress called him on it. You couldn't find a backbone in the House GOP caucus with an MRI.

And his letter reflects his understanding that every institution, indeed, every person, who challenges the Dear Leader must be destroyed.

The free press? An "Enemy of the People," he said -- the same day someone sent pipe bombs to CNN.

The federal judiciary ? "So-called judges" or the "Mexican judge" or "a complete and total disaster."

The US intelligence community? Their alleged leaks are, in Trump's words , "something that Nazi Germany would have done and did do."

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Allies who shed blood alongside Americans are scorned. Dictators and strongmen are coddled. Putin is praised. All in a day's work for Mr. Trump.

The letter is Trump's governing philosophy distilled. He is a wannabe autocrat, who has made his goal clear: to remake America as he has remade the Republican Party -- turning a once-proud, strong party into a gaggle of sycophantic lickspittles. His rage for Speaker Pelosi is boundless because she stands up to him. His letter is a window not into a troubled psyche, but something much worse.