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 flawedit was "completely irresponsible."

That ishow 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 thatthe 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.

Itseems that one's views on the Senate's rights and privilegescan dependon 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.

The unavoidable existence of the Senate

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 rightbut (arguably) the responsibilityto 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 hasraised questions about how or whether the upper chamber should impose limits on itself. Some critics imaginean independent Senate might run wild and become a major obstacle to legislation passed by the House.

A modicum of self awareness could be enough to tell senators that, at some point, they might risk inflaming publicoutrage by thwarting the will of the House. Peter Harder, the first senator to hold the title of "government representative," suggested a few potential ground rules that the newly independent Senate might heed in an essay published in 2018.

For government bills, Harder said the Senate should adopt the "Salisbury doctrine." That convention, established in the United Kingdom, says the upper chamber should not absolutely block legislation that implements a commitment previously made in the governing party's election platform.

As for private members' legislation, Harder said the Senate should at least ensure every such bill comes to a vote and senators should not exercise a "pocket veto" by leaving private members' bills to languish in the upper chamber, as has happened in the past.

How C-234 is a preview of debates to come

By Harder's logic, C-234 is due for a final vote at some point. But Conservative claims that the Senate is not moving fast enough on C-234 would be on firmer ground if Conservative senators had not been regularly accused of delaying various pieces of legislation over the last several years.

C-234 has been before the Senate for eight months. A Liberal bill to change the words of the national anthem spent 19 months in the Senate before finally being passed.

In light of C-311's demise in 2010, it would be at least a little awkward (or a little late)for Conservatives to argue now that the Senate should never defeat a private member's bill. It's also possible thata Senateamendment could doom the billindirectlyas Conservative Sen. Denise Batters warned during debate in the Senate last week.

If senators amend the bill, it gets sent back to the House. At that point, the Liberal government whose members voted almost unanimously against the bill could try to keep it from advancing again.

That might be a legitimate point of concern for the bill's supporters. Senators also could argue that they can't (or shouldn't) be held accountable for the actions (or inaction) of the House.(Debate in the Senate has also includedallegations of bullyingandone Conservative senator apologizing for his behaviour.)

Conservatives also have argued that the Senate should feel compelled to pass C-234 because it is a matter of tax policy. But it's not clear how often the Senate has ever restricted itself along those lines as recently as 2013, senators amended a bill that involved the Income Tax Act.

Viewed from one angle, C-234 is another milestone in Parliament's continuing experiment with an independent Senate. But all of the complaints and concerns being raised by the Conservatives might also be viewed as a prelude.

Until now, the independent Senate has largely interacted with legislation passed or supported by a Liberal government. Sooner or later there will be a Conservative government. And the grumblingfrom Conservatives over the past few weeks might be a preview of how much (or how little) tolerance a Conservative government will have for senatorial input.

The Liberals, as originators of this new era of Senate independence, have been largely willing to tolerate Senate amendments. Conservatives, who still insist senators should somehow be elected, may be less patient.

The Senate, as ever, will have to justify its actions or decide which actions can be justified.

But whether the Senate exercises its indisputable right to pass, defeat or amend C-234, this is unlikely to be the last time the newly independent Red Chamber finds itself facing pressure from a demanding Conservative leader.