In its common definition, the job of president of the United States is to deliver peace and prosperity. Donald Trump is doing well on both fronts, so let’s impeach the bastard!

As insane as it sounds, that and only that is what many Democrats have in mind. Impeachment, or death by a thousand investigations, is the heart of their plan.

For proof, eliminate their desire to remove Trump from office and see if you can pinpoint anything else with broad Dem support. Some advocate for open borders, others for tax hikes or Medicare-for-all, but ending the Trump presidency ASAP is the glue holding the party together.

It unites the leadership with the rank and file, including many of the socialist-leaning newcomers. Its migration from the far-out fringe to a daily talking point among party faithful and their national media lapdogs represents a breathtaking development.

The implications are staggering — and a potential disaster for America.

An immediate result is that good news for the country is bad news for the impeachment caucus. Friday’s staggering jobs report — 312,000 people added to payrolls in December — was a blockbuster that sent stocks soaring.

Similarly, federal reserve chairman Jay Powell suggested for the first time a possible pause in interest rate hikes, which is music to the ears of business as well as potential homebuyers and investors.

The day’s events were added proof that the great American economic engine, despite some hiccups, is still roaring and creating jobs and wealth. Wages are rising far faster than inflation and, as the Wall Street Journal notes, 473,000 manufacturing jobs have been added during Trump’s presidency, while that sector lost 210,000 jobs during Barack Obama’s regulatory onslaught.

As Obama once said, elections have consequences. Sometimes they are good consequences.

Yet the Democrat making the biggest news Friday was a foul-mouthed new congress member from Michigan, Rashida Tlaib, who had celebrated her swearing-in by promising that “we’re going to impeach the motherf–ker.” The leftist crowd was jubilant.

Never in modern times has there been such a disconnect between the opposition party and the realities of national life. The very talk of removing Trump, without evidence of an impeachable offense, is a stick in the eye to history and most Americans.

To be clear, the disconnect is not the product of policy differences, though they exist too. This is instead a mass outbreak of Trump Derangement Syndrome that, for those infected, can be cured only by undoing the results of the 2016 election.

And if by some lightning strike they succeed, then what? Impeach President Mike Pence, too?

How does any of this help the country address its infrastructure needs, reform entitlement programs or ensure better schools and more opportunities? And what message does it send to our allies and adversaries about America’s resolve?

The questions answer themselves. The relentless fixation on impeachment is a destructive decision that sacrifices national progress and security on the altar of partisan madness.

Almost as disconcerting is that, among some Dems, the 2020 race for president already has begun, nearly two years before Election Day and just seven weeks after the midterms that were supposed to settle things.

The relentless fixation on impeachment is a destructive decision that sacrifices national progress and security on the altar of partisan madness.

But Sen. Elizabeth Warren couldn’t wait, using the last day of 2018 to say she is running. Others, especially a handful in the Senate, are sure to follow quickly, lest Warren have the spotlight to herself.

All politics, all the time is great fodder for the media and consultant class, but is usually a disaster when it comes to getting things done for the country. On that score, good luck to Speaker Nancy Pelosi and Senate minority leader Chuck Schumer trying to get the impeachers and presidential wannabes to focus on the details of legislation.

Both groups will be focused only on donors and party activists and making sure they are on the left flank of their rivals. “No” is always a safe vote because nobody ever got elected saying “yes” to controversial ideas or, in this case, voting for anything that Trump can claim as a victory.

Paralysis by politics, of course, is a bipartisan disease, and Trump is not immune. His decision to force a partial government shutdown over border wall funding followed warnings that he was on the verge of betraying a key promise to his supporters.

But that doesn’t make both sides equally wrong. Trump is clearly right that there can be no national security without border security and that border security is not possible without barriers to block and deter illegal crossers.

He made a coherent case for that at his press conference where he tried to put a happy face on his meeting with congressional leaders. But Schumer and Pelosi would rather share a glass of hemlock than give Trump a win on the wall.

Unfortunately, they are leaders in name only. If they had the courage to stand up to the lynch mob setting their party’s agenda, they would have spent the last two years negotiating with a president who likes nothing better than cutting deals.

But by caving into the demands of the fanatical resistance movement, Schumer and Pelosi painted their party — and the nation — into a corner. Unless they inject sanity into the chaos, the shutdown will be a mere taste of the trouble ahead.