If the Washington establishment thought President Donald Trump would turn into one of them, they were seriously mistaken.

Trump signaled in his first day of office that he’s not going to go along with the power brokers in the nation’s capital — many of them standing right behind him on the inaugural stage.

The new president’s defiant speech after taking the oath of office was a jab at every lawmaker, lobbyist, ex-president, network pundit and editorial writer who scoffed at Trump’s campaign and message and worked to defeat him.

But now it’s time to deliver.

Trump can’t spend too much time celebrating his inaugural. He needs to take advantage of the momentum from his turn in the spotlight and parade down Pennsylvania Avenue before the establishment starts fighting back.

And they will.

Trump will be under major pressure in the coming weeks to give up some of his campaign promises and play ball with Congress. And State Department diplomats will want him to continue the same failed policies of the Bush and Obama eras.

So far, there’s no sign of that.

It’s clear that Trump intends to govern much the same way he campaigned — as an unapologetic populist not afraid to use bluster and ruffle some feathers. And he will continue to use social media to get out his message above the whine of the mainstream media.

His opening speech was remarkably devoid of partisanship or soaring rhetoric about “hope” or “a thousand points of light.” It’s not often you hear the word “carnage” in an inaugural address. He clearly didn’t run it by Doris Kearns Goodwin.

The network anchors and pundits were mortified — seemingly stunned by Trump’s refusal to deliver empty promises like healing the nation and reaching out to Democrats and those who opposed him.

But Trump didn’t reach out to Republicans either, which no doubt infuriated more than a few GOP lifers in Congress.

Trump instead used almost all of his 16 minutes to pay tribute to downtrodden and dismissed voters — “forgotten” Americans who fueled his victory — and no doubt they were cheering the new president’s words.

“This is your day. This is your celebration,” Trump said in a speech that was notable for its brevity — something the new president is not exactly known for.

Those who were looking for some kind of uplifting message or pat on the back were no doubt chagrined.

That includes a lot of people on the inaugural stage, including former Presidents Obama, Bush and Clinton, whose machines have ruled Washington for decades. Aside from a nod to Obama for his “magnificent” help in the transition, the former presidents didn’t get much love from Trump. His depiction of the establishment using the government for their own benefit was an indirect slap at all who came before him.

But that’s Donald Trump. Get over it.