Allegations of crack-smoking are usually enough to push even the most tenacious of politicians from public office. Not so for Toronto Mayor Rob Ford, who has been dogged by a drug scandal since May, but point-blank refuses to step down — even in the face of this week's revelation by city police chief Bill Blair that his force is in possession of a video that apparently shows the mayor hitting a crack pipe.

The scandal first came to light when the Toronto Star said it had been approached by drug dealers trying to sell the video. Gawker subsequently raised $200,000 in an online campaign to buy it — but then the tape mysteriously vanished.

Now it's back. While Blair has admitted the video doesn't contain enough evidence to lay charges against Ford, the fact that the mayor of Canada's largest city has apparently been caught on camera smoking crack is probably reason enough for most voters to expect him to go.

But try telling him that. "I have no reason to resign," Ford insisted, to the disbelief of many, at a strange, Halloween-themed press conference:

Of course, he isn't the first politician to remain defiant when confronted with what seems like a fait accompli. Here are four others who just didn't know when to quit:

1. Marion Barry
The original crack-smoking mayor, Barry was busted in 1990 in an FBI sting operation that saw a cooperating informant lure Barry into a hotel room with promises of sex and drugs. A video captured Barry smoking from a crack pipe, as well as his now-infamous words, "Bitch set me up," after FBI agents swarmed the room. But Barry did not relinquish office even as he fought the charges in a highly publicized trial, which eventually resulted in a six-month prison sentence.

Indeed, Barry went on to run a successful City Council campaign in 1992 once he got out of prison, campaigning under the slogan: "He May Not Be Perfect, But He's Perfect for D.C." He then astounded the nation in 1994 by winning the mayor's office once more. Rob Ford, take note.

2. Bob Filner
Another mayor; different scandal. Faced with accusations of sexual harassment from a staggering 17 women — including a former staff member who said he had repeatedly demanded kisses, trapped her in a headlock, and asked her to come to work without panties — the San Diego mayor admitted "inappropriate" behavior, but still refused to step down. Instead, he said, he would undergo two weeks of intensive therapy at a behavioral clinic, before returning to office:

Unfortunately for Filner, that wasn't enough for the City Council. Instead, he was forced to resign as part of a deal in which he avoided jail time. This month, the mayor pleaded guilty to three charges of false imprisonment and battery, and will serve three years of probation.

3. Anthony Weiner
Weiner, aka Carlos Danger, has proved to be one of the most stubborn of leeches when it comes to political power. It all began in 2011, when the then-congressman was caught sending explicit photos of himself to strangers on Twitter. At first, Weiner tried to deny sending the images. Then he attempted to pass them off as a "joke." Finally, he gave a press conference in which he admitted to "terrible mistakes," but defiantly stated he wouldn't be resigning anytime soon. Yes, he had lied, he said. Yes, he had caused his loved ones pain. But that was hardly reason to step down:

Until ten days later, when he did just that. Not wounded enough by the first scandal, he then of course decided to give his career another shot by entering this year's race for New York mayor. And we all know how that ended:

4. Herman Cain
In late October 2011, when Cain was in the middle of his presidential run, Politico reported that at least two employees had accused the Republican candidate of sexual harassment and misconduct during his time as CEO of the National Restaurant Association. Cain denied the allegations, and ignored calls to pull out of the race. Instead, he decided on a novel approach to distract those calling for his resignation. A little gospel, anyone?

But then — rather inconveniently for Cain — a woman called Ginger White claimed she had been having an affair with the Republican for 13 years, right up to the point that he announced he was running for president. Days later, he dropped out of the race.

The lesson for Ford? Unless you're Marion Barry, you may not be able to avoid the inevitable — no matter how hard you try.