The fight over the Senate's handling of the carbon tax is a portent of things to come

Some time ago, the leader of an opposition party stood during question period and lamented that "unelected senators" had thwarted the "will of the House of Commons" by defeating a private member's bill. 

In response, the prime minister stood and expressed the government's view that the bill, even though it had passed the House, was so deeply flawed it was "completely irresponsible."

That is how Stephen Harper justified the move by Conservative senators to defeat C-311 — a climate change bill sponsored and supported by the NDP and its then-leader, Jack Layton, that had managed to pass the House because the Conservatives did not have a majority.

Almost exactly 13 years after the Senate killed C-311, the upper chamber began third-reading debate on C-234, a Conservative MP's bill that would create a new exemption from the federal carbon tax for certain farming activities. The bill passed the House because there were not enough Liberal votes to defeat it.

The fact that the Senate hasn't yet passed the bill — and is even considering amending it — is causing some consternation on the Conservative side of the House.

On Tuesday, Conservative leader Pierre Poilievre moved a motion calling on "the unelected Senate to immediately pass C-234 … as passed by the democratically elected House."

"The prime minister has deployed his carbon tax minister to pressure senators to block that bill, in an undemocratic attack on the prerogative of the commoners to decide who pays what," Poilievre told the House.

It seems that one's views on the Senate's rights and privileges can depend on where one happens to be sitting in Parliament at the time. At least one major aspect of the Senate has changed in the past 13 years — it has a mind of its own now.

It is an indisputable fact that the Senate exists, however much some might wish it otherwise. The drafters of Canada's founding documents also made the Senate a fundamental part of Canada's constitutional architecture — so much so that, in the judgment of the Supreme Court, abolishing the Red Chamber would require the unanimous consent of the provinces.

Unless or until someone can muster the support necessary to either reform or excise the Senate, it will retain not just the right but (arguably) the responsibility to closely scrutinize legislation passed by the House of Commons. The only question is how far it should go in doing so.

Between 2006 and 2015, when Harper's Conservatives were in power, the Senate was relatively reluctant to assert itself. It amended just 14 bills passed by the House during that time — 11 government bills and three private members' bills.

Justin Trudeau came into office having already ejected Liberal senators from the Liberal parliamentary caucus. He proceeded to fulfil his commitment to appoint independent senators who would be relatively free to do as they pleased. Strictly speaking, only three senators have some relationship with the sitting Liberal government: the government representative in the Senate, the legislative deputy to the government representative and the government liaison. 

The result has been a much more active upper chamber. In the past eight years, the Senate has amended 29 bills, including one private member's bill.

The emergence of a more assertive Senate — one where most senators are not tied to the major political parties — inevitably has raised questions about how or whether the upper chamber should impose limits on itself. Some critics imagine an independent Senate might run wild and become a major obstacle to legislation passed by the House.