Since the beginning of the 2015 federal election campaign, New Democratic Party (NDP) Leader Thomas Mulcair has championed decriminalization of marijuana.

On Aug. 21, Mulcair told supporters: "I want to make sure that everybody understands that the NDP's position is decriminalization the minute we form government." On Oct. 13, he reaffirmed that position and added, "when we get elected on October 19, no one ever gets a criminal record for possession or use of marijuana."

But can the NDP decriminalize cannabis on day one? Yes and no.

First, the bad news if you're a supporter of decriminalization. Changing any Canadian law requires the same six legislative steps. How long that process takes varies, but it certainly won't be finished overnight. So the NDP can introduce a decriminalization bill immediately, but they can't finalize it then.

The good news? Mulcair's claim that no one will be arrested for possession after Oct. 19 could hold true. But that's ultimately up to law enforcers, not the prime minister. At least, that's what happened the last time decriminalization nearly became law in Canada.

In 2003, Prime Minister Jean Chrétien's Liberal government sponsored Bill C-38, a decriminalization motion that gained support from every opposition party except the Conservatives. When the bill gained momentum in the House of Commons, some law enforcers stopped charging Canadians for possession of cannabis.

"Everybody was waiting for what was going to happen," said Terry McLaren, the former president of the Ontario Association of Chiefs of Police. "There'd be no use clogging up the court system with that decriminalization bill there."

But there was no formal, nationwide order to stop making marijuana busts, though some police forces took matters into their own hands. In Toronto, then-police chief Julian Fantino ordered police to stop arresting people for possession. Meanwhile, Tom Kaye - McLaren's predecessor as OACP president - told Ontario police to "use discretion in situations that involve the simple possession of marijuana."

Fantino and Kaye were responding to Bill C-38, as well as a controversial lower-court ruling in Ontario that invalidated the enforcement of cannabis laws in the province. The Ontario Court of Appeal later rewrote cannabis laws to make the province's legislation valid.

So Mulcair can assume some police forces will stop making arrests, but he can't expect all of them will while the decriminalization bill makes its way through the federal legislative process.

Mulcair might also want to be cautious about promising to end cannabis busts immediately considering the way in which the last decriminalization effort backfired.

Bill C-38 died when Chrétien prorogued parliament in 2003. The new Liberal Prime Minister Paul Martin reintroduced decriminalization legislation, but it died when his government fell in November 2005. The Conservatives, who opposed reforming cannabis laws all along, did not revive plans to decriminalize.

Some policing experts believed the confusion subsequently caused a spike in arrests in 2006, because some younger cannabis users didn't realize it was still a criminal office.

'The Rebuttal' is a regular feature that takes the statements of politicians and tests them against the facts at hand. Do you have suggestions for statements we should fact-check. Leave a comment below. Twitter: @civilized_life. Facebook: Civilized

h/t CBC, The Star, Cannabis News.