We have learned a lot from the first two days of the Trump administration. There are facts — things that are indisputably the case — and there are “alternative facts” — things that someone in the White House wants to be true.

That’s why the newly sworn-in president decided to spend much of the weekend attacking the media for honest reporting on the size of the crowds who came to Washington this weekend.

Here are the facts: Crowd scientists employed by The New York Times estimate that about 160,000 gathered on the National Mall to see Donald Trump sworn in as the 45th president of the United States. That’s a big crowd, but considerably less than the 1 million-plus who turned out to see Obama sworn in the first time, or the estimated 450,000 who packed the Mall and the streets of Washington on Saturday to affirm their commitment to women’s rights.

But, so what? That doesn’t make Trump’s victory in November any less significant. He is still the president of the United States, the single most powerful person in the world. He still has a lot of work to do.

The voters turned up for him when it mattered, on Election Day. The size of the crowd should not have mattered.

But apparently it did. Trump himself went to CIA headquarters and told employees that the real inauguration crowd had been much bigger than what had been reported by a media that he said is biased against him. Then he sent press secretary Sean Spicer out to hector the White House press corps with a series of demonstrably false statements about the size of the crowd, the number of riders on the capital’s Metro system, the protective covering of the Mall’s grass and the type of security used.

Those easily disproven statements are what Trump adviser Kellyanne Conway called “alternative facts” on “Meet the Press” on Sunday, forcing a befuddled Chuck Todd to sputter, “Alternative facts are not facts. They are falsehoods!”

Which is true, but beside the point. The real question in not about the numbers on the Mall. It should be: What else might these high-level administration figures be willing to lie about if they are going to spend their first days in office creating “alternative facts” about something as inconsequential as the size of a crowd?

And when the same spokesman has to look into a camera to say that our nation is under attack, how are we supposed to know which are the real facts and which are the “alternative facts”?

President Trump has been hired to do vitally important public business every day, and that job will not get easier when a substantial percentage of the country decides that it cannot trust him. He can say he’s fighting back against the media, but when he’s fighting against the truth, he’s destroying his administration’s credibility.

Once that’s gone, you can’t get it back. And that is a fact.