"Both our countries have very similar regulations regarding issuance of visas for citizens who have violated the law," the consul, Lewis A. Lukens, wrote to Feldmar in September. "The issue here is not the writing of an article, but the taking of controlled substances. I hear from American citizens all the time with decades-old DUI convictions who are barred from entry into Canada and who must apply for waivers. Same thing here."

The waiver process would require a lawyer, several thousand dollars and dishonesty, Feldmar said. He would have to say he has been rehabilitated.

"Rehabilitated from what?" Feldmar asked. "It's degrading, literally degrading."

Ethan Nadelmann, the executive director of the Drug Policy Alliance, which works to ease drug penalties, said Feldmar's case proves how arbitrary American drug policy can be.

"Roughly a majority of the population of the United States between the ages of 18 and 58 has violated a drug law at least once," Nadelmann said, and there is no reason to think that Canadians and other foreigners of a certain age have experimented much less.

It has been a long, strange trip from the Summer of Love to the Age of Terror, from excluding people based on actual criminal convictions to turning them away based on a border guard's Google search. The first approach is rooted in due process and enhances the nation's security. The second is profoundly arbitrary and effectively punishes not past drug use but honest discourse about it.

"I should warn people that the electronic footprint you leave on the Net will be used against you," Feldmar said. "It cannot be erased."