Let’s agree that President Trump’s travel ban on visitors from seven nations was a sensible idea hobbled by flaws, especially regarding green card holders and dual citizens. Let’s also agree we haven’t seen a rollout this clumsy since the debut of ObamaCare, which was far more serious because it penalized millions of Americans while Trump’s order inconvenienced hundreds of foreign nationals.

Still, we can assume, based on past performance, that Trump will learn from the mistakes. His fierce determination to be a successful president cannot co-exist with rookie blunders.

But what about the other players in the drama? Can we say the media will now correct its excess of bile and cover Trump as a legitimate president and not as an invasive species?

No, no, no. On the contrary, we must say that Trump aide Steve Bannon was on target when he called the Washington media “the opposition party.”

Don’t take his word for it. Stick a toe into the toxic sludge that passes for straight-news coverage in the Washington Post, the New York Times and others.

Look for the use of tell words like “Muslim ban” to describe an executive order that is no such thing. Look for hero worship of protesters, immigrants, refugees, lawyers rushing to the barricades and congressional critics.

Look, too, at the Twitter feeds of editors and reporters from those papers and the major networks. You’ll see their embrace of everything anti-Trump, further evidence they are part of a movement to obstruct the president, not cover him.

Consider, too, their rediscovered love for Republican Sen. John McCain, a man they ignored during the eight-year reign of their savior, Barack Obama. McCain is again the good maverick because he is bucking the media’s permanent enemy, Republicans.

Yet if the media is the opposition party, what is the Democratic Party? It’s supposed to be the loyal opposition, using checks and balances to restrain the president and the excess of one-party rule.

Unfortunately, the Dems are following a dangerously different path. Starting with a wide boycott of the inauguration and including their boycott of committee votes on Trump’s cabinet and their pledge to filibuster any Supreme Court nominee, Democrats resemble a party fomenting a secession movement.

Some call it Trump Derangement Syndrome, but that’s too kind. It’s not a temporarily insane reaction, it’s a calculated plan to wreck the presidency, whatever the cost to the country.

Things never seen in the modern era are now rapidly becoming common. Impeachment talk already is rumbling in the party’s hothouses, and Trump was met with a lawsuit the minute he took the oath.

Chuck Schumer and Nancy Pelosi, the top Dems in Congress, led a raucous demonstration Monday night, as if they are community organizers. And Obama couldn’t bear the irrelevance after eight days out of office and felt compelled to encourage disruptions.

This is Third World behavior and it’s now the M.O. of one of America’s two political parties.

Then there’s California, the epicenter of Dem strength. Radicals there, spurred on by pro-Mexico immigrants, are ginning up an effort to split from the United States and they might get a proposal on the ballot. I say we take their wine and let them go.

If California secedes and its 55 electoral votes come off the board, Dems will never win another American election. On the other hand, Hillary Clinton could become president of the breakaway state and the rest of us would be free of the Clinton stain.

Secession is one way the swamp could drain itself. Sally Yates’ way is another.

The acting attorney general was rightfully sacked the instant after she climbed a soapbox and refused to defend Trump’s executive order in court. It would have been a more admirable gesture if she had the decency to resign. Instead, she thought she could defy the president and keep the job.

Her choice was not a minor act of insubordination. It was a public challenge to the constitutional authority of the president, a power left to Congress and the judiciary.

As a result, she was shunned and hid in disgrace. Oh, wait, that’s what would happen in a better world.

In this one, Democrats hailed her as a “patriot” amid predictions a political star is born.

My prediction is that Dems are digging their own grave and their revolt against his legitimacy will, in the short term at least, boost Trump’s popularity. Most Americans will conclude he is honestly trying to fulfill the mandate he won and that the fevered rush to destroy him is neither principled nor patriotic.

There is a catch: Our cultural impatience won’t give Trump endless time or big room for error. He must pick his fights with discretion and wage them with smart, methodical moves that bring clear results.

Equally key, he can’t become a prisoner of Washington. While social media is important, he must get out of town regularly to meet people where they live and remind them that he’s fighting their fights.

He should continue to court core Democrats, especially members of manufacturing unions and open-minded black and Latino voters.

If he does all that, and if he’s lucky, America will be great again. That’s what matters.

Mayor’s final chance

Perhaps it was just a poor choice of words, or was it a Freudian slip? Either way, Mayor Bill de Blasio used a curious phrase in describing his planned meeting with federal prosecutors.

“This set of allegations just doesn’t comport with who I am,” he said on NY1. He said he will be “setting the record straight” on investigations into whether he created an illegal pay-to-play scheme.

A fair reading of the “set of allegations” phrase, along with what we know, suggests de Blasio is getting a last chance to convince the feds he shouldn’t face specific criminal charges.

If that’s the case, de Blasio is likely doomed. Such final meetings are routine as prosecutors make sure they haven’t missed important evidence that would gut the case later.

Legal arguments usually fail and political ones always do. New evidence is the only escape hatch.

Unless the mayor is holding an ace in the hole, he’d better be careful. Otherwise, he could talk himself into a perjury charge as well.

City tax bid hits home

You think your money is yours, but New York City Deputy Mayor Alicia Glen begs to differ.

City Hall wants a new “mansion tax” of 2.5 percent on any house sale above $2 million. Asked if she thought the tax might crimp sales, Glen told the Wall Street Journal the criticism is ridiculous and added, “If you look at how much money we’ve left on the table for the past two years while this thing went sideways, it makes me nuts.”

In other words, be grateful the city let you keep its money for two years. Now hand it over.

Word of trouble

Headline: “North African gangs attack Chinese migrants in Paris.”

Another great moment in globalism.