On Wednesday, Sen. Ted Cruz (R-TX) made a little Halloween joke, tweeting a coded message patterned after the Zodiac, a notorious serial killer from the San Francisco Bay Area.

Displaying that he has a sense of humor about himself is part of a larger Cruz project over the past year to, under pressure from a surprisingly well-funded Beto O'Rourke campaign, render himself not so toxically disliked by his colleagues. Not so long ago, the former House Speaker John Boehner even called him a “miserable son of a bitch.” Now he's showing he can laugh about his bad reputation.

Still, the fact remains that his reputation is really bad and that Republicans are only rallying to his side because they recognize that losing a Senate seat in Texas would be a disaster.

So why does this keep coming up?

1) Who is the Zodiac Killer?

If I knew, I would be informing the proper authorities and not writing about it here.

The name, however, is used to denote an unknown serial killer who operated in northern California in the late 1960s and early ’70s. He murdered at least five people (and left two surviving victims) and is regarded as a leading suspect in four more murders. The Zodiac Killer corresponded with authorities and the public via letters and postcards sent to media organizations, occasionally cryptographically encoded, in which he claimed a total of 37 victims.

The perpetrator of these crimes was never identified, and the combination of the mystery with the publicity-seeking and cinematic flourishes — like signing his letters with a distinctive symbol and communicating in code — have made the killings a subject of national fascination for decades.

There are several books about the Zodiac Killer, one of which, by Robert Graysmith, was adapted into a 2007 film directed by David Fincher. The theory of Graysmith's book — endorsed to a limited extent by Fincher's film — is that the killer was Arthur Leigh Allen (who died in 1992), whom Graysmith links to the killings via a raft of circumstantial evidence.

But Allen's culpability is contradicted by the fragmentary forensic evidence available. Allen's DNA does not match DNA recovered from one of the Zodiac Killer's stamps (Graysmith replies that the evidence was not stored with a view toward later DNA technology), and handwriting analysis indicates huge differences between the killer's letters and any known writings of Allen's.

The point is the Zodiac Killer's true identity was never discovered, and he may well still be at large. Since the killings and the letters stopped, it seems likely that he abandoned murder as a hobby and moved into other social deviant behaviors like attending Princeton, working for George W. Bush, or spoiling the GOP's best-laid plans to stop Donald Trump.

2) Is Ted Cruz the Zodiac Killer?

In all seriousness and as best we can tell, no. An exhaustive investigation by the Washington Post's Philip Bump reveals that Cruz was born in 1970, while the Zodiac Killer's first confirmed murder occurred in 1968. Therefore Cruz is not the Zodiac Killer.

Cruz's birth certificate establishes this pretty clearly.

The same document also confirms that Cruz was born in Canada (specifically the province of Alberta, which is known informally as the Texas of Canada), and that his name is Rafael rather than Ted. (As Rafael is also my father's name, I kind of wish Cruz went by Rafael, since it would make the Spanish spelling of this name better known in the United States and reduce the number of times his name gets misspelled "Raphael" like he's a Teenage Mutant Ninja Turtle or a Renaissance painter.)

On the other hand, who even knows what an authentic Canadian birth certificate looks like? It could be a forgery. After all, a person capable of perpetrating the Zodiac Killer's crimes — and getting away with it — could probably fake some paperwork.

3) Why do people say Cruz is the Zodiac Killer?

It's a joke. The joke appears to have originated way back in 2013 on the @RedPillAmerica Twitter account, which quipped during Cruz’s speech at the Conservative Political Action Conference that the subject of his address was going to be a confession of responsibility for the Zodiac Killer’s crimes.

#CPAC Alert: Ted Cruz is speaking!! His speech is titled: 'This Is The Zodiac Speaking' — Red Pill America (@RedPillAmerica) March 14, 2013

A few months later, in October, there was a two-week government shutdown largely as a result of a legislative strategy that Cruz hatched. His prominence grew. And it grew again as a result of his 2016 presidential campaign.

Cruz’s stature in American politics provided occasion for more jokes about Ted Cruz. And one thing that happens on the internet is that when a joke has been made enough times it becomes a meme, and simply repeating the meme becomes a way of making a joke.

4) Okay, but what’s the joke? Why is this funny?

Many people think you can't explain jokes, or that even trying to explain them ruins them.

The 18th-century philosopher Immanuel Kant disagreed, explicating humor thusly:

Suppose this story to be told: An Indian at the table of an Englishman in Surat, when he saw a bottle of ale opened and all the beer turned into froth and overflowing, testified his great astonishment with many exclamations. When the Englishman asked him, "What is there in this to astonish you so much?" he answered, "I am not at all astonished that it should flow out, but I do wonder how you ever got it in." At this story we laugh, and it gives us hearty pleasure; not because we deem ourselves cleverer than this ignorant man, or because of anything else in it that we note as satisfactory to the Understanding, but because our expectation was strained for a time and then was suddenly dissipated into nothing.

In Cruz’s case, what happens is that you expect to see someone criticizing him for his smarmy speaking style or his retrograde politics, but then your expectation winds up being strained for a time with the accusation that he is an infamous serial killer. When you realize that he is too young, dissipation strikes.

In addition, Cruz fits the basic serial killer profile. His colleagues in the GOP Senate caucus don’t like him. He's a loner, ostracized by the key social networks among which he operates. Maybe he also kills people for pleasure? It’s difficult to say.

5) Do people really hate Ted Cruz that much?

They sure seem to! After all, a couple years ago Lindsey Graham, a Republican senator from South Carolina, said of his Texas colleague: “If you killed Ted Cruz on the floor of the Senate, and the trial was in the Senate, nobody would convict you.”

Graham was, of course, joking, but it’s a telling kind of joke. Few people Cruz works with have anything good to say about him or endorsed him when he ran for president.

They really, really dislike him. What’s more, given that he’s a notorious serial killer, people really wouldn’t convict you if you killed him. You'd just be doing what had to be done to bring a dangerous criminal to justice.

6) Seriously, though, why do people hate Cruz?

On one level, it’s about the fact that he’s a cold-blooded killer who has evaded justice for decades. But on another level, Cruz has generated an enormous amount of ill will in Republican establishment circles by launching lines of political argument that they believe he knows to be false as part of a cynical scheme of self-promotion.

The standard Cruz move during the Obama years was to take some objective that was uncontroversial in conservative circles — repeal Obamacare, defund Planned Parenthood — but also totally unacceptable to the Obama administration and not especially effective as a wedge issue, then decide that congressional Republicans should achieve this goal all on their own. Cruz’s pitch was that if Republicans simply exhibited sufficient solidarity and refused to fund the government until Obama gave in to their goals, then Republicans would win. Then when it didn’t work, Cruz blamed his fellow Republicans rather than blaming President Obama.

The upshot of this was to create individual political problems for lots of Republican politicians and undermine the GOP’s effort to do the one thing that could actually achieve these goals: win a presidential election.

In other words, they see Cruz as really the worst of all possible Washington worlds — an extremist who really just poses as more ideologically pure than colleagues, advancing his own personal agenda while setting back the movement's cause.

That's the kind of reputation that lands you friendless and alone, wandering the streets of Washington searching for the most dangerous game.

It's not you. Bad doors are everywhere.