I do not know how to explain what I just watched.

It should be easy. Donald Trump introduced Indiana Gov. Mike Pence as his running mate. There it is. One sentence. Eleven words. But that doesn’t explain what happened any better than "I spent a few hours letting lysergic acid diethylamide mimic serotonin in my brain" explains an acid trip. What just happened was weird, and it was important.

Back in May, E.J. Dionne wrote that the hardest thing about covering Donald Trump would be "staying shocked." Watching him, day after day, week after week, month after month, the temptation would be to normalize his behavior, "to move Trump into the political mainstream."

But today helped. Trump’s introduction of Mike Pence was shocking. Forget the political mainstream. What happened today sat outside the mainstream for normal human behavior.

It began in irony. Before Pence, before Trump, there was an empty podium and the Rolling Stones blasting through the speakers. It had been widely reported that few top Republicans were willing to serve as Trump’s running mate. It had been widely reported that Trump was unsure about Pence, that he had regretted the decision almost as soon as he made it, that he had sought ways to reverse himself. Hours before the announcement, Trump tweeted that Pence was "my first choice from the start!" which is a thing presidential candidates typically do not need to say.

Look forward to introducing Governor Mike Pence (who has done a spectacular job in the great State of Indiana). My first choice from start! — Donald J. Trump (@realDonaldTrump) July 16, 2016

So there we were. Waiting for Trump and Pence to emerge. And what Rolling Stones song did the campaign choose? What did we all hear, over and over again, as we waited for Trump to introduce Mike Pence, his "first choice from the start!"?

"You can’t always get what you want..."

Now back to Mike Pence...

What started as farce continued as farce. Trump emerged without Pence. He spoke, alone, at a podium adorned with his name but not Pence’s. And then Trump proceeded to talk about himself for 28 minutes. There is no other way to say this than to say it: It was the single most bizarre, impulsive, narcissistic performance I have ever seen from a major politician.

There is no way I will be able to properly described Trump’s speech to you. You should really just go and watch it yourself.

I can tell you that he rambled, but that doesn’t do it justice. He spoke about Hillary Clinton, about himself, about his victories. He talked about crushing the Republican establishment in the primaries and talking to a buddy building plants in Mexico. He bragged about the beautiful hotel he is building in Washington, DC, and patted himself on the back for his foreign policy foresight over the years.

Every five minutes or so, he seemed to remember, just for a moment, like a man trying and failing to wake from a dream, that he was there to introduce Mike Pence, and so he would say something like, "Now back to Mike Pence," but then he would slip back again and tell another anecdote about himself.

Even when he did mention Pence, he often managed to say exactly the wrong thing. "One of the big reasons I chose Mike is party unity, I have to be honest," Trump admitted midway through his speech, at the moment another candidate would have said, "I chose Mike because he’ll be a great president." Trump then segued into a riff on how thoroughly he had humiliated the Republican establishment in state after state. Thus he managed to turn Pence from a peace offering into a head on a pike, a warning to all who might come after.

He can barely stick with a Pence thought for more than five seconds. — Nick Confessore (@nickconfessore) July 16, 2016

When Trump finally stuck to Pence, at the end of his lengthy speech, he seemed robotic, bored, restless. He recited Pence’s accomplishment like he was reading his Wikipedia page for the first time, inserting little snippets of meta-commentary and quick jabs as if to keep himself interested.

The final humiliation was yet to come: Trump introduced Pence and then immediately, unusually, walked off the stage, leaving Pence alone at the podium.

Trump is a great entertainer. But he’s not running for host of America: The Show.

As with all things Trump, the speech was funny and magnetic. The guy is great TV. But it was also wrong. It was a blue standup set delivered at a board of directors meeting, a cruel roast offered at a child’s birthday party. Selecting and introducing a vice president is a heavy duty in American politics; it is the most power one person will ever have to potentially choose the leader of the free world.

But Trump couldn’t see past himself to match the moment. The cameras turned on, and he did the thing he always does, perhaps the only thing he can do: He put on a show and made himself the star.

Trump introducing Pence with a long list of ways Trump is awesome, has been awesome, and will continue to be awesome in the future — Benjy Sarlin (@BenjySarlin) July 16, 2016

On Friday night, as the attempted coup in Turkey progressed, Matt Yglesias wrote about his efforts to imagine Trump in the Oval Office as the crisis unfolded. "Picture Donald Trump on a series of calls with advisers and heads of government from around the region, and inside the NATO alliance, devising a constructive response to a coup attempt in Turkey," he wrote. "Good luck."

On Saturday morning, as Trump prepared to brag about his hotel business before introducing Pence, he briefly turned to the issue. Keep in mind he had the whole night to prepare.

"So many friends in Turkey," Trump said. "Great people, amazing people. We wish them well. A lot of anguish last night, but hopefully it will all work out." Ladies and gentlemen, the next president of the United States, Donald Trump!

I know many who want to support Donald Trump, who fear Clinton ideologically or simply dislike her personally, and so they are hoping, hoping, hoping that Trump will reveal a new side to himself, that he will prove himself equal to the responsibilities he seeks to absorb. But he’s been given that opportunity again and again, and he keeps failing it.

This was a fun speech to watch, and insofar as the presidential campaign is one of America’s favorite reality television series, Donald Trump is an outstanding participant. But this was also a scary speech to watch, and insofar as the presidential campaign is a test to see who has the character, the discipline, and the seriousness to be president of the United States, Trump is failing it. We need to stay shocked.

Watch: Why Trump can't change and become "moderate"