Hillary Clinton revealed a disconcerting flaw when she fell ill at a 9/11 event Sunday.

She showed us that she is human. Not the superhuman we have demanded she be, only human.

That’s something a woman can’t afford to disclose when she’s competing in a race that always has been dominated by men.

One of the lessons women learn early in life is that they’ve got to be tough in order to succeed. Fragility can be a fatal flaw that has brought an end to many a promising career. And whatever you do, we’re told, never let them see you cry. The bigger bitch you are at work, the more your peers will respect you. These are rules from the workplace playbook women memorize before we’re even out of high school.

Now that we have our first female presidential nominee from a major party, we are hearing about other rules that apply to women seeking the nation’s highest office: Never let them see you cough or take a sip of water to clear your throat, and for God’s sake, don’t stumble while getting into your campaign SUV.

Pictures of the would-be commander in chief being supported by a staff member as she abruptly left the 9/11 memorial event in New York put Clinton’s health on showcase in her contentious race against Donald Trump. And the video showing her nearly collapsing into the arms of Secret Service agents as she stepped into her vehicle was enough to convince some that she is hiding a serious illness.

advertisement | advertise on newsday

The fact that her doctor said later that Clinton had been diagnosed with pneumonia a couple of days before was met with skepticism. Her doctor’s note carried far less weight that the one Trump’s physician quickly scribbled giving him a clean bill of health while the candidate waited outside in a car.

At age 68, Clinton is two years younger than Trump. But by America’s sexist double standard, she’s the equivalent to 100 while he’s considered to still have the virility of a 30-year-old. As a result, her health is deemed more vulnerable than even the Republican Party’s beloved Ronald Reagan, who was 69 when first elected president.

Former New York Mayor Rudy Giuliani summed up Clinton’s health this way after she attended a recent news conference with New York police officers. She “looked tired” and she “looked sick,” he said.

The not-so-subtle point is that Clinton is an old woman, way past her prime and usefulness. Rather than trying to be president, she should be content sitting at home, spending her twilight years enjoying her grandchildren.

When it comes to electing a female head of state, the U.S. lags behind other countries, even some that are considered far less progressive. At this moment, there are more than a dozen female presidents, ruling countries such as Chile, South Korea and Liberia. In Germany, Chancellor Angela Merkel has been calling the shots for more than a decade. And in Great Britain, Theresa May just took over as prime minister, following a path set by Margaret Thatcher in 1979.

But in the U.S., we are still lukewarm to the idea of having a woman at the helm of our government. Part of the reason is that many Americans still don’t consider women equal to men.

We work the same jobs as men, but with less pay. We work as hard as men do, but often don’t get the same opportunities for advancement. And as the recent debacle at Fox News shows, women are still subjected to sexual harassment and often treated as though they are a disposable commodity in the workplace.

So when Hillary Clinton stumbled on Sunday, she let her guard down and showed her weakness, her vulnerability. In that moment, it was easy to forget what an accomplished statesman she is, that she has served in the U.S. Senate and held one of the most important jobs in our democracy - secretary of state.

advertisement | advertise on newsday

She didn’t look like a seasoned diplomat. In the eyes of some, she was merely a woman and a sickly one at that. Even some of her ardent supporters panicked. Is she strong enough to stand up to bullies like Vladimir Putin and loose cannons like Kim Jong Un? Is she a match for our most ardent foe, ISIS?

There’s no question that Clinton is smart. She can run circles around Trump when it comes to, well, any issue. But for some people, that still isn’t good enough. In order to feel like America is still on top, they need a man in the forefront. Trump proves that for some, any man will do.

So why did Clinton continue on the campaign trail, even when her doctor advised her to get some rest? Why did she open herself up to more questions about her health, her stamina, her ability to serve as the first female president?

She kept going because she’s a woman, a strong one at that. And a woman can’t afford to stay home and nurse a cold - or even recover from pneumonia - when she’s trying to break through a glass ceiling.

Dahleen Glanton is a columnist for the Chicago Tribune.