Washington — When dealing with a political figure who faces allegations of sexual assault, financial misdeeds and obstruction of justice, it is difficult to sort out the greatest damage to our public life. But a strong case can be made that it is the assault on truth.

This was again on display in a recent interview of President Trump by NBC News’ Chuck Todd. When asked his reaction to losing the popular vote in 2016, Trump returned to the narrative that he had been robbed of a popular vote victory through fraud. “I’ll say something that, again, is controversial,” said Trump. “There were a lot of votes cast that I don’t believe. I look at California … Take a look at their settlement where California admitted to a million votes.”

Trump’s claim is not just “controversial.” It is a whole-cloth fabrication by the most ambitious fabulist in presidential history. The “settlement” to which Trump was apparently referencing was a judicial order for the state of California to remove about a million inactive voters from its registration list. This can in no way be interpreted as a million fraudulent votes cast for Hillary Clinton in 2016 (which still would not have won Trump California or the national popular vote).

Is Trump’s determination to inhabit his self-blown truth bubble a psychological compulsion or a political ploy? That is an interesting question, but an academic one. Each explanation reinforces the other.

Most of Trump’s boldest lies are devoted to protecting himself from facts that diminish him. So, his net worth must be exaggerated, no matter what his tax returns might say. His inaugural crowd must be larger than Barack Obama’s, no matter what aerial photographs clearly show. He was cheated out of a popular vote victory, no matter what the evidence indicates.

Sometimes Trump’s self-serving deceptions are hard for followers to keep straight. The Mueller report, for example, was both dismissed as the illegitimate work of Democratic agents, and embraced as complete vindication on matters of collusion and obstruction. Even though the explanations are inconsistent, they are unified by Trump’s broader purpose: the bending of reality to serve his self-perception.

Some kind of personal pathology seems to be at work. Trump’s epistemology is not so much relativistic as solipsistic. He has a bottomless need to project himself as wealthier, stronger, smarter and better than he actually is. This is a sign, not of strength, but of psychological fragility. Desperation for the illusion of mastery is the evidence of deep brokenness. It indicates a hunger for affirmation that reality will never fill. This encourages both self-delusion and the spinning of elaborate, self-serving lies.

Why should these attributes bother us in a president? Because narcissism is not merely a stronger form of personal ambition. It is a different and distorted way of perceiving the world. Part of psychological wholeness — and of responsible political leadership — is the ability to consider reality from someone else’s perspective. But Trump seems incapable of escaping the small, dark cell of his own immediate needs and desires. He can’t see the world from the standpoint of an ally or an enemy. He seems immune to empathy for a minority facing prejudice, or a refugee fleeing from oppression, or a migrant child separated from his or her parents.

And Trump appears to accept no moral standards external to his interests. Every principle or truth is judged in relation to the welfare of his person. There is apparently nothing he won’t say to maintain the mythology that he is the winningest winner there ever was or will be. This means that he careens from crisis to crisis without moral guide rails.

Trump is not only speaking a series of lies. He is inviting millions of loyalists to live in a political reality conjured by his deceptions. Any news critical of him is fake. Any agitprop that supports him — even by the purveyors of conspiracy theories — is to be believed. And any election he might lose is fraudulent.

Not long ago, I sat on a plane next to a knowledgeable and articulate Trump supporter. The talk turned to the Mueller report and I mentioned that Robert Mueller was awarded the Bronze Star for his bravery in Vietnam. “How do you know that?” snapped my conversation partner. I sputtered something about reading it in multiple, reliable sources. She remained unconvinced.

How is any political conversation or policy discussion possible when citizens inhabit separate universes of truth and meaning? This is Trump’s most dangerous innovation: epistemology as cult of personality.

— Michael Gerson is a columnist for Washington Post Writers Group.