The stock market was supposed to collapse if Donald Trump became president. That was the prevailing view right before the election when almost everyone assumed that he wouldn’t be.

It was also a good scare tactic for those who were maybe a little concerned that this guy with the crazy hair had even a minute chance of pulling off an upset. Surely, people wouldn’t vote for a guy who could cost them money, his opponents figured.

And when it became apparent pretty early on election night that Trump would be president, the Dow Jones industrial average sank about 800 points in the futures market — until a rescue effort was made by Trump’s friend billionaire Carl Icahn and other forces unknown.

Icahn said the drop in the market was stupid and that he was a buyer because he believed in Trump.

Well, Trump has been president for less than a week, and whaddya know? Today the Dow breached the henceforth invincible 20,000 level for the first time ever.

Pop the corks. And throw the Gatorade over Coach’s head. It’s happy days again.

As I’ve been explaining for a long time, stock prices are very high. And the market is dangerous for anyone but the very brave and the willingly careless. Corporate profits have been weak and revenues weaker.

The market’s price-to-earnings ratio — the traditional gauge for market bloat — is already off the charts. And it might even be in the stratosphere if companies have been fooling with their earnings calculations as much as some people suspect.

But this week Trump did stuff that might make the market’s current levels make sense. I emphasize the word “might” because what Trump has done might also lead to Wall Street’s next collapse.

Let’s go with the optimistic view first because, as you know, the champagne is already in the glasses and you shouldn’t poop a party that so many people are already enjoying.

Trump, the businessman, has been quite clear all week that he will keep his pledge to attempt to rescue a US economy that has been listless for nearly a decade. He has pulled out of a trade agreement in Asia, browbeat companies that are manufacturing in Mexico and — with the swipe of a pen — OK’d pipelines in the Midwest that’ll create jobs.

I know, I know. The environmentalists are up in arms. That’s a different story entirely, and it will be told many times over the long run.

But the more immediate effect of the new president’s first week is a feeling that he might get the economy moving a little faster. And that could be good for companies, which in turn is good for the stock market.

There are a lot of things that could go wrong with President Trump’s actions. For one thing, I don’t think he has completely thought through the fight he is picking with China. That country owns more than a trillion dollars in US government bonds and can cause American interest rates to soar by just uttering the word “sell.”

If borrowing costs go up, the economy will slow down.

And the Asian markets whose trade pact we now aren’t going to join are important to the profits of many American companies. So that move could also backfire in that way.

And, of course, there is a certain segment of US voters and elected officials who don’t want Trump to succeed at anything. So his nay-saying opponents might not even allow Wall Street its Dow 20,000 celebration before they start guerrilla warfare against the new president’s actions.

Still, sip some bubbly and enjoy the moment. The Dow may not even stay over 20,000 until the end of today. But there’s no reason you can’t celebrate at halftime when your team is ahead.

Just don’t celebrate too much.