Critics of Donald Trump worry what would happen if a man with little regard for the Constitution and a willingness to impose his personal will on a hot-button issue like immigration became president.

This isn’t a far-fetched scenario — in fact, it has already happened. A deadlocked Supreme Court let stand a lower court order blocking President Obama’s unilateral bid to grant amnesty to millions of illegal immigrants in a wholly outrageous violation of our constitutional norms.

President Obama’s order was so flagrantly lawless that he had repeatedly denied he had the power to act on his own — until he did.

The “deferred action” program in question granted amnesty to the illegal-immigrant parents of US-born children and expanded a previous executive amnesty for illegal-immigrants who came here before age 16. The administration claimed the program was merely an exercise in prosecutorial discretion. In reality, it was a new legal dispensation, giving a broad category of illegal immigrants work permits, Social Security numbers and driver’s licenses, among other benefits.

In his huffy remarks after the Supreme Court decision, Obama said when Congress refused to act on so-called comprehensive immigration reform he “was left with little choice but to take steps within my existing authority to make our immigration system smarter, fairer and more just.”

But there is no clause in the Constitution giving the president the power to legislate in the absence of congressional enactments. The president’s own sweeping description of the supposed benefits of his action — a smarter, fairer, more just system — implies its breadth.

It certainly doesn’t sound like a mere act of discretion around the edges — and it isn’t. The appeals court noted that nearly 150 pages of instructions were issued on how to carry out the president’s previous executive amnesty, and only about 5 percent of more than 700,000 applications were denied.

The president of the union representing the immigration workers charged with processing those applications said DHS worked to ensure that they were “rubberstamped.” President Obama himself had said DHS officials who didn’t implement his latest edict would face “consequences.”

So much for discretion.

In his post-decision statement, the president referred to our “broken” immigration system, a favorite cliché of supporters of amnesty. The brokenness of the system, though, is largely a function of the longstanding refusal by the federal government to enforce our existing immigration laws. If we didn’t enforce our tax or environmental laws, they’d be broken, too.

Obama is said by his critics on the open-borders left to be the Deporter-in-Chief, but this is a misnomer wrapped in an act of statistical legerdemain. The Obama administration began counting deportations differently to get the numbers up. Obama himself has admitted that this accounting gimmick is misleading.

The truth is that interior enforcement has been gutted. John Sandweg, former acting director of Immigration and Customs Enforcement, has said, “If you are a run-of-the-mill immigrant here illegally, your odds of getting deported are close to zero.” Even the deportation of criminal aliens, supposedly the priority of the administration, has been declining.

The assurance that Obama issued after the Supreme Court decision that enforcement priorities won’t change is certainly correct — the enforcement priority will continue to be non-enforcement.

The conventional wisdom is that better border controls and a weak economy have checked the flow of illegal immigrants, but the numbers are beginning to tell a different story.

According to data from the Center for Immigration Studies, illegal immigration in 2014 and 2015 — with other countries picking up the slack from Mexico — is significantly up from the levels it was at over the prior two years. Overall, the number of new legal and illegal immigrants is now higher than before the 2007 recession.

No matter how high-handed President Obama has been in defying the separation of powers to get his way on immigration, an even more lawless president beckons. Hillary Clinton has pledged to go even further.