Events in Iowa this week show the Democratic Party is skidding off the rails. Nineteen Democrats running for president took the stage at Cedar Rapids on Sunday to woo voters. It was a circus of left-wingers going bonkers for things most Americans don’t want.

The frontrunners back abortion any time before birth, abolishing ICE (the immigration enforcement agency), outlawing gas-burning cars, shutting down fossil-fuel industries that employ millions and redistributing wealth. These White House contenders are veering far left, even though polls show half their own party’s voters aren’t “liberal.”

It’s a worrisome spectacle. For 150 years, our two-party system has provided political stability envied by the rest of the world. Republicans and Democrats put forward broad agendas to compete for the widest number of voters. When one party wins, the other cedes power and cooperates in governing.

Not this time. The Democratic contenders are espousing policies so far left, they leave even moderately liberal members of their own party behind. They are also vowing to destroy their Republican opponent, President Trump.

The frontrunner, Vice President Biden, skipped Sunday’s candidate circus, but his three nearest challengers — Senators Bernie Sanders and Liz Warren and South Bend, Indiana’s mayor, Pete Buttigieg — took aim at the former veep, warning against picking a moderate.“We’re not going to win by playing it safe,” said Mayor Pete. Sanders railed against a “middle ground” that “changes nothing.”

So far, Iowans aren’t convinced. Polling shows Biden almost 10 points ahead of the radicals, because he has name recognition and he’s electable. But Biden’s morphing, dumping long-held positions and careering left on abortion and climate.

For decades, Mr. Biden opposed taxpayer-funded abortions, citing his Catholic faith. He even authored the 1981 Biden amendment banning foreign aid from paying for abortion research. Last week, thoough, he flip-flopped, ­announcing he now supports federal funding. Does he actually have principles?

Most Americans, including Democrats, see abortion as a wrenching, complicated issue. An NPR/Marist poll finds only 18% support third-trimester abortion. Yet every senator running for president voted against a bill requiring doctors to help ­infants who survive a late-term abortion.

Senator Kirsten Gillibrand says there is no room in the party “for a Democratic candidate who does not support women’s full reproductive freedom.” That’s slamming the door on a majority of voters.

On climate, Mr. Biden’s already capitulated to the Green New Dealers. Last week he announced his plan to force America into zero net carbon emissions by 2050, including regulating gasoline-powered cars out of existence. A sure loser with heartland voters working in the auto and fossil-fuel industries.

For years, Mr. Biden and mainstream Democrats like Presidents Clinton and Obama called for strong borders. The left dubbed Mr. Obama the “Deporter-in-Chief.” Yet now Mr. Biden’s under assault for his past views. Expect another flip-flop.

Today most elected Democrats are siding with illegal immigrants, instead of with the public. When the House was asked to pass $4.5 billion in border-relief funding last week, with most of it for food, medical care, and schooling for children, Democrats refused, because a sliver of the funds would pay for enforcement — proof Democrats are for open borders.

Yet polling shows 54% of Americans want more done to stop illegal immigration. Last week, they got it. Mr. Trump, the dealmaker, used tariffs to coax Mexico into stopping the caravans before they reach the American border. His success left Dems like Mr. Sanders mumbling platitudes about not ­going to “verbal war” with our allies.

Meanwhile, 11 Democratic presidential contenders are calling for the House to impeach Mr. Trump. On Tuesday, Mr. Biden arrived in Iowa, preposterously declaring Mr. Trump an “existential threat to America.” Speaker Nancy Pelosi says she wants Mr. Trump in prison. It’s banana republic talk, the kind for which Democrats berated Mr. Trump. It undermines America’s envied two-party system.

Democrats eyeing the White House need to get real. By writing off moderate members of their own party, they’re boosting Mr. Trump’s chances of reelection. Then again, a Trump victory may be the gut punch that brings the Democratic Party to its senses.

Ms. McCaughey is a former lieutenant governor of New York. This column first appeared in the New York Post.