With less than five months to go before a federal election, Conservatives are making a special effort to establish just how dimly they view Justin Trudeau's time as prime minister.

This week, their lament was about taxes and the apparent plight of ordinary Canadians under the Trudeau government's allegedly high-tax agenda.

"When will the government realize that Canadians are taxed to the max and cannot afford to pay any more?" Pierre Poilievre asked on Tuesday.

Two days later, it was Lisa Raitt's turn to worry aloud. "Can the government please give comfort to Canadian families, and assure them that it will not continuously look to them for more taxes?" she asked.

In response to such attacks, the Liberals tend to note that federal transfers — notably the Canada Child Benefit — have been enhanced to increase the financial support they provide. According to the government's math, the average middle class family is better off by $2,000 compared to the situation in 2015.

The Conservatives, so far, remain unmollified.

Part of the Conservative argument is that Trudeau's Liberals will surely raise taxes if they continue to govern after October. Conservatives remain adamant that the Trudeau government has engaged already in a confiscatory raid upon the public's wallets and bank accounts.

How Harper won the taxation argument

But Raitt and Poilievre — two former cabinet ministers from Stephen Harper's government — might try to take more pride in the current situation. If anything, the tax system they left behind has proved fairly durable.

The relative "burden" of taxes can be assessed in a number of ways, but the federal government's official accounts offer a relatively straightforward measure that allows for comparisons across years: annual federal tax revenue as a share of Canada's Gross Domestic Product.

For 2014-2015 — the last full fiscal year of Stephen Harper's government — tax revenue as a share of GDP was 11.5 per cent.

For 2018-2019 — after nearly four full years of Justin Trudeau's government — tax revenue as a share of GDP is projected to be 12.7 per cent. In subsequent years, according to the government's own numbers, it's forecast to settle around 12.4 per cent.

That 0.9 -point increase is not nothing. But it's still below what the federal government was taking in when Harper's Conservatives came to office in 2006. It's even further below what the federal government was raising at the respective peaks of the Mulroney and Chrétien years.

For 1999-2000, for instance, total tax revenue reached 14.5 per cent of GDP — the highest point of the last 35 years.

What followed was a steady and significant decline. First, the Liberal government cut taxes. At the end of Paul Martin's time as prime minister, total tax revenues stood at 13.2 per cent of GDP.

Stephen Harper's tax cuts were designed in part to make it hard for subsequent governments to reverse them. (The Canadian Press)

Then the Conservative government cut taxes. Stephen Harper's Conservatives reduced the GST by two points and decreased the corporate tax rate from 21 per cent to 15 per cent. A half point was taken off the lowest bracket for personal income taxes, Tax Free Savings Accounts were created and a half dozen tax credits designed to appeal to potential Conservative voters.

Between 1983 and 2006, annual federal revenue averaged 13.3 per cent of GDP. But under Harper's government, federal tax revenues, measured as a share of GDP, reached a modern low of 11.4 per cent in the 2011-2012 fiscal year. This is what recently led Alex Himelfarb, a former clerk of the Privy Council, to lament the long-term trend toward austerity.

A $30 billion hole

According to an analysis conducted by the office of the parliamentary budget officer, the changes of the Harper era resulted in annual federal revenues being reduced by $30 billion. For the sake of comparison, the total amount of funding committed to the Canada Child Benefit is currently $24 billion.

This was not unintentional. Stephen Harper's Conservatives were quite happy to reduce the federal government's capacity. And, as those numbers show, they were rather successful at it.

Key to that goal was cutting taxes that a future government would be reluctant to restore — the GST in particular. Reducing that tax by two points cut annual federal revenues by $14 billion. But no major party leader has since proposed reversing that cut.

Trudeau's Liberals campaigned on one specific increase — a new bracket at the top of the income scale that raised taxes on the richest Canadians. After coming to office, they also repealed a handful of the Harper government's tax credits and have since followed through on promises to restrict other tax advantages that mostly benefit wealthy households — including income-splitting for couples, an exemption for stock options and the use of private corporations. (You might remember the last of those changes for the yelling that ensued.)

The Trudeau government did, of course, introduce a carbon levy, at least where provincial governments refused to introduce their own. But the revenue from that levy is being directly rebated to individuals and businesses.

Meanwhile, the GST is still at five per cent, the corporate tax rate is still at 15 per cent and, as the Conservatives promised to do, the small business rate has been reduced to nine per cent. For good measure, the Liberals also cut the second income tax bracket from 22 per cent to 20.5 per cent. (And the claim that the current deficit will necessitate future tax increases is debatable.)

But at 12.4 per cent, the Liberals would end up almost exactly midway between Harper's historic low and the pre-Harper average.

That the Trudeau Liberals managed to preside over any increase in federal revenues is something of an accomplishment, given how much easier it is to cut taxes than to raise them. Even Jagmeet Singh's New Democrats aren't (yet?) calling for a dramatic hike.

The Conservatives, of course, will continue to condemn any deviation from their historic low. But all change is relative. There's at least as much room to wonder why federal taxes couldn't be higher.