In the early hours after this year’s Brexit vote, the top Google searches on the topic by shocked Britons were “what does it mean to leave the EU” and “what is the EU.”

Don’t let this happen here.

Now that James B. Comey has dedicated the FBI to the election of Donald Trump, a remote possibility is a serious prospect. But we don’t have to wonder what the first 100 days of a Trump presidency would look like. Trump has given a clear picture of what he plans, and the rest would be filled in by events beyond Trump’s control.

Among things you can expect: a trade war with China and Mexico, a restarting of Iran’s nuclear program, millions losing their health insurance, the start of mass deportations, a possible military standoff with China in the South China Sea and North Korea, the resumption of waterboarding, the use of federal agencies to go after Hillary Clinton and other Trump critics, the spectacle of the commander in chief suing women who have accused him of sexual misconduct and a constitutional crisis as the president of the United States attempts to disqualify the federal judge in a fraud suit against him because the judge is Latino.

Oh, and the Fed would be audited, and guns would once again be allowed in schools — thank heavens.

Donald Trump gestures after speaking at a campaign rally. (Logan Cyrus/Agencce France-Presse via Getty Images)

[History will remember which Republicans failed the Trump test]

Trump has said that on his first day in office he would label China “a currency manipulator” — kicking off punitive tariffs. Trump said he would seek a 45 percent tariff on Chinese imports. Likewise, he would on his first day announce that he would renegotiate or (more likely) withdraw from the North American Free Trade Agreement. He favors 35 percent tariffs on Mexican imports.

China and Mexico, thrown into recession, would likely retaliate by blocking U.S. businesses from their markets. In the ensuing trade war, American consumers would be unable to purchase products they rely on, and inflation would soar.

American businesses would lose hundreds of billions of dollars in exports. A Moody’s report done for The Post predicts a net cost to the United States of 7 million jobs. Recession would come within a year — unless further economic shocks bring about a 1930s-style depression.

And where would such a shock come from? Well, Trump has said he would ask Congress, also on his first day, to repeal Obamacare. This would mean the loss of health insurance for 24 million Americans, and mass chaos.

At the same time, Trump would deliver a shock to labor markets: He would, on his first day, begin the deportation of more than 2 million “criminal illegal immigrants.” The liberal Center for American Progress calculates this would cost $20.1 billion, and there’s only enough funding currently to deport 400,000 per year.

Simultaneously, Trump pledges to deliver an immediate blow to local-government finances, cutting off hundreds of millions of dollars in public safety and other funds to “sanctuary cities.” U.S. universities and laboratories would be hit by Trump’s pledge to cancel payments to U.N. climate-change programs, the Center for American Progress says. Huge tax cuts that Trump pledged would require either massive cuts in government spending (and resulting job loss) or vast increase in debt.

The backdrop for these economic shocks: international chaos. Many Trump early-days promises — halting immigration from terrorist-prone countries, renegotiating NATO terms and the Iran nuclear accord, pulling out of the Trans-Pacific Partnership and the Paris climate-change agreement — would open rifts with allies in Europe, Asia and the Middle East.

[Fellow millennials: I know you’re frustrated. Vote anyway.]

As trade wars spread, shocks to the economy mounted and allies retreated, the new president would be distracted by legal proceedings. Though “Crooked Hillary” gets the attention, a judge in New Jersey last month ruled that there is probable cause to investigate a complaint of official misconduct against Gov. Chris Christie — the head of Trump’s would-be transition — because of his role in the “Bridgegate” scandal. Ties to Russia by two Trump loyalists are reportedly under federal examination.

Trump University is facing multiple investigations and class-action suits accusing it of fraud. One such suit is scheduled to go to trial on Nov. 28 before U.S. District Judge Gonzalo Curiel. Trump called Indiana-born Curiel “Mexican” and said the judge can’t be impartial because of his ethnicity.

Trump has threatened to use the power of the presidency against Curiel, much as he has threatened to use it against Clinton and the media. “They ought to look into Judge Curiel,” he said, adding, “We will come back in November. Wouldn’t that be wild if I am president and come back and do a civil case? . . . This is called life, folks.”

This is life in the early days of a Trump presidency: economic shock, international instability and constitutional crisis as Trump makes the presidency his plaything.

Don’t say you weren’t warned.

Twitter: @Milbank

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