The most important social and legal change in Canada during 2018 will almost certainly be the legalization of marijuana. This move, the boldest by the Trudeau government so far, will end almost a century of prohibition of cannabis that has resulted in a great deal of misery while delivering few benefits in return.

The House of Commons has passed two laws that will make the consumption of marijuana legal while toughening the rules against abuse of the drug. The prime minister now says his goal to put them into effect by “next summer.”

But it’s far from clear that will actually happen. Conservatives in the Senate are threatening to derail the entire project by stretching out debate on legalization in the Upper Chamber for many months – past the original deadline of July, and possibly deep into next fall.

They should cease and desist. The appointed Senate has a constitutional job to do in reviewing legislation passed by the elected Commons. But deliberately thwarting the will of MPs by manipulating the arcane rules of the Senate is something else again.

The Senate officially began debate on Bill C-45, the Cannabis Act, and C-46, which would tighten rules on impaired driving related to marijuana use, at the end of November, as soon as the Commons passed them

So it had seven months to vet the bills – ample time if senators are honestly determined to fulfill their duties while respecting the will of the Commons. But debate in the Senate is far from straightforward and since the Conservatives form the single biggest group on party lines (ever since Justin Trudeau freed Liberal senators from party discipline) they can control the pace of debate.

Independent Senator Tony Dean has a better idea. He’s the sponsor of Bill C-45 in the Senate and proposes bringing in a “structured” debate for this important legislation. It would give senators a chance to examine the new laws, but according to a timetable that would bring it to a vote well before July 1.

“I’m not talking about limiting or rushing discussion,” Dean wrote recently. “I’m talking about organizing discussion – a predictable, formulated debate.” That kind of debate was successfully used in the Senate to examine another contentious piece of legislation, the law on medical assistance in dying.

The government representative in the Upper Chamber, Peter Harder, has also proposed bringing ministers involved in the issue to testify before the Senate in early February so senators can question them. All that would give senators a good chance to offer their “sober second thought” on the cannabis bills in a timely manner.

Let’s recall what’s at stake here. The current marijuana laws criminalize thousands of Canadians for using a relatively harmless drug. Aside from medical marijuana, pot is sold mostly through gang-run black markets and the proceeds aren’t taxed.

There is legitimate concern about marijuana’s effects on young people, but prohibition hasn’t worked very well there either. Canada has one of the highest rates of pot use among the young – higher than some other countries like the Netherlands where it is tolerated. Nor has legalization in some U.S. states led to a spike in consumption among youth.

Legalization with strict rules around distribution and sales, however, is complicated. The provinces are busy putting sales networks in place to meet the federal deadline, which involves locating outlets, signing legal agreements, hiring staff, preparing public education campaigns, and much more.

To kick this can down the road for months longer – perhaps until the end of 2018 or even longer – would disrupt all that planning.

Even worse, the Conservative senators are also threatening to delay the related Bill C-46, which will bring in stricter rules around driving while impaired – by either alcohol or marijuana.

Leaving aside the wisdom of legalizing cannabis, delaying the impaired driving law is indefensible. In an open letter to senators, MADD Canada (formerly Mothers Against Drunk Driving) points out that “drugs are present in fatal crashes nearly twice as often as alcohol.” They are calling on the Senate to pass C-46 without delay.

At the moment, Conservatives have 34 members in the Senate, compared to 39 Independents and just 15 Liberals. That gives the Conservative minority unusual power to manipulate the chamber’s rules.

But if they do that to defy the elected Commons and delay these laws unnecessarily, their party and the entire Senate will be discredited.

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The Upper Chamber should do its job – in a timely, organized fashion that allows the best possible law on legalization to be adopted on the government’s schedule.

Correction – December 27, 2017: This article was edited from a previous version that mistakenly said cannabis is legal in the Netherlands. In fact, it is not legal but is tolerated.

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