If you aren’t seriously contemplating the biggest black swan event in American electoral history, you aren’t paying attention.

Fifteen months ago, Donald Trump was a reality-TV star with a spotty business record and a weird penchant for proclaiming that he was on the verge of running for president. Now, he’s perhaps a few big breaks and a couple of sterling debate performances away from being elected 45th president of the United States.

Trump has no experience in elected office and, unlike past nonpoliticians elected president, hasn’t won a major war. He barely has a national campaign. He perhaps knows less about public affairs than the average congressman. He has repeatedly advertised his thin-skinned vindictiveness and is trampling on basic political norms.

No major political party has ever nominated anyone like this. If Trump were to prevail, it would make Barack Obama’s unlikely rise from unknown state senator to first African-American president of the United States in about four years look like a boringly conventional political trajectory.

Trump now has a legitimate shot at winning the general election because he got the lucky draw of at least the second-worst presidential nominee in recent memory and, pending how she fares over the next two months, perhaps the worst.

All it took for Trump to wipe away most of Hillary Clinton’s lead was acting like a somewhat normal presidential candidate. Have a meeting with a foreign leader. Give some policy speeches. Read from a teleprompter at rallies. Use his NPR voice when appropriate.

None of this required strategic genius, only a decision not to throw away the election with repeated episodes of self-indulgent stupidity. Democrats should be feeling a creeping sense of panic:

— They are trying to win with a candidate who is loathed and distrusted and has few redeeming qualities. As Yuval Levin, editor of the journal National Affairs, points out, corrupt and dishonest politicians are often entertaining, and dull politicians are usually earnest and honest. Hillary manages to be both boring and corrupt. If she decided to sit out the rest of the campaign and rely on surrogates to hit the trail, she might do no worse and perhaps better.

— No one can be certain that her health is what the campaign says it is. If Hillary did have a more serious condition than allergies and walking pneumonia, does anyone believe the Clintons would be forthright about it? Even if nothing else ails her, if Clinton has another episode in public like the one on Sept. 11, the bottom might fall out.

— President Obama probably can’t close Hillary’s enthusiasm gap. For entirely understandable reasons (dull, inauthentic and old), the Obama coalition isn’t excited by Clinton. Obama is an adept campaigner, but there is no evidence Obama ever successfully transferred enthusiasm for himself to another candidate.

— If the kitchen sink hasn’t killed off Trump, what else is there? The Clinton campaign has already used his greatest hits of most offensive statements in countless TV ads. If none of this has sunk Trump, what’s left that is going to have a new and different shock value?

— A compelling Trump debate performance could change perceptions of his suitability to be commander in chief. Hillary is trouncing Trump on this attribute by a 2-to-1 margin. If Trump shows up and seems plausible during the biggest moment of the campaign, he could vastly improve his standing on this basic question of readiness.

All this said, Hillary probably still has an advantage. Presumably, she won’t be as snakebit the rest of the campaign as she has been the past two weeks. She has a campaign and Trump doesn’t, and that must count for something. Demographics favor her. But if Trump can hoist himself over the bar of acceptability, he might give the voting public enough permission to make this the change election it is naturally inclined to be.

A Trump victory may not be likely, but it isn’t far-fetched. And no, stranger things haven’t happened.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.