The other day I received an email that read: “Why is it not surprising that someone named Rubin would be a full fledged lib-tard? Go (expletive) yourself you biased piece of (expletive).”

No surprise, the sender was a Trump fan. Of course, not all Trump fans who write me are so vile or anti-Semitic, but most are — and many are worse. They feel empowered by a candidate who encourages them to attack their opponents.

This is the kind of hatred stoked by the rancid rhetoric of Donald Trump.

So I ask those Republicans who are on the fence, or Democrats who might vote for a third party, do you really want a demagogue in the White House?

The U.S. president is the face of our country to the world. Our allies are aghast that a man of Trump’s character might be elected president. Our adversaries are delighted because they see it as a sign that our democracy is crumbling.

Meantime, Trump’s ugly operating style has already debased the nature of political campaigning — in ways that will haunt the country.

Perhaps you have become inured to Trump’s racist, sexist tweets and threats to opponents. His ugly insults flow so fast and furious they may seem like a new normal to you.

Wake up! It is not normal to break all the basic rules of civility that enable our system to function. Trump’s tirades against judges, the press and against our system of voting undermine our democracy. His refusal to treat political opponents with a minimum of decency threatens to rip our electoral system apart.

It is not normal to belittle opponents within your own party, calling them losers or liars or wacko, nor is it normal to slander their family members. Remember when Trump tweeted that Jeb Bush’s wife was an illegal immigrant (she isn’t) and linked Ted Cruz’s father to the Kennedy assassination?

Trump has made threats and insults against any critics an essential part of his campaign plan, and of his endless Twitter feed. In an astonishing display of hypocrisy last week, Melania Trump said she would focus on combating social-media bullying as first lady. She never mentioned that she shares a home with the nation’s leading cyber-bully.

Imagine the tweet-obsessed Trump pumping out his nastiness every night from the White House bedroom. What kind of example would that set?

It is not normal for a candidate to scapegoat entire groups of people, including blacks, Mexicans and immigrants. It is not normal to constantly demean women — with trash talk of groping, menstrual bleeding and weight.

Before Trump, could you have imagined a candidate who boasts publicly about his sex life, his adultery, his several wives and the size of his privates? What kind of man does this?

Is it possible that this candidate’s vulgarity and immorality have become the new normal for you?

If so, let me remind you it is not normal for a candidate to insult Gold Star families and war heroes. Who could imagine that a GOP nominee could call Sen. John McCain a “loser” because he was a POW?

And it is not normal for anyone to insult the disabled in the most disgusting fashion. You may recall Trump’s gross imitation of a disabled reporter. Did you know Trump also mocked conservative columnist and paraplegic Charles Krauthammer for not being able to get dressed?

But beyond his foul character, let’s get to the most dangerous realm of Trump’s aberrant behavior.

It is not normal for a major candidate to promote racism and talk anti-Semitic trash. Trump’s rhetoric emboldens rabid white nationalists to come out in the open, where once they might have stuck to unsigned emails. The candidate endorses websites filled with paranoid conspiracy theories that stoke the rage of supporters (his campaign CEO, Steve Bannon, comes from one such site, Breitbart).

Which brings us to the worst of the new normal that Trump would introduce if he wins.

It is not normal for a would-be president to promote violence against opponents — and anyone he dislikes.

Trump rails against reporters and protesters at rallies, encouraging his fans to take action. “I’d like to punch him in the face” is the Trump style.

Compare this with President Barack Obama’s graceful call at a rally Friday for supporters to treat a Trump protester with respect. In another of his endless, blatant falsehoods, Trump accused Obama of “yelling” at the man. It is not normal to be a pathological liar.

Yet the Donald goes further. He threatens to arrest Hillary Clinton as if he were a Russian dictator, and leads chants to “lock her up.” This is not normal behavior. It would horrify Ronald Reagan.

And do you consider this normal? Trump has hinted that gun-rights supporters could take matters into their own hands if Clinton is elected. The implication was clear: If they think she is tampering with the Second Amendment, they can take her out.

Is this the America you want? You cannot kid yourself that such behavior is normal. This is the stuff of banana republics. Or Germany in the 1930s.

Of course, not all Trump supporters are part of this hard core. You may be one of many voters who are still leaning toward Trump because you dislike Hillary Clinton.

Yet, whatever your feelings about Clinton, she will not empower America’s darkest instincts. She respects democratic norms and institutions.

Trump is a demagogue who has unleashed the darkest passions of many Americans. The people who write me these emails are waiting in the wings for him to enter the White House.

A vote for Trump is a vote for his new normal. You have to decide whether you will help this demagogue win.

— Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.