Size of Justin Trudeau's government breaks records, for better and worse

When parliamentarians return to work at the House of Commons on Thursday, those on the opposition benches will find a majority Liberal government sitting on the other side of the aisle for the first time since 2005.

Two weeks ago, we looked at how the newly elected Conservative opposition stacked up against its predecessors in that role. But how does Justin Trudeau's governing side measure up against past governments?

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The Liberals captured 184 seats and 39.5 per cent of the vote on Oct. 19. In raw numbers, the Liberals have the largest governing caucus since 1984, when Brian Mulroney's Progressive Conservatives won 211 seats. Beyond that one, only two other governments have ever had more MPs than the current one. Trudeau's is also the government with the most female MPs in Canadian history.

But the size of the Commons has not held constant. Those 184 seats occupy 54.4 per cent of the House of Commons, a share that ranks the Liberals' electoral performance just 24th out of the 42 elections that have taken place since 1867. With governing caucuses over that time averaging 56.8 per cent of the House, that gives Trudeau's team a slightly below-average size.

(Note that in the tables and calculations below, the 1925 election has been excluded. The Liberals under Mackenzie King were defeated at the polls in that election by Arthur Meighen's Conservatives, but, with the initial support of the Progressive Party, the Liberals remained in power. Machinations in the House eventually led to the King-Byng Affair and the short-lived Meighen government that went down to defeat in 1926.)

The Liberals as a new government

Compared with other first-term governments, however, Trudeau's Liberals stack up better.

While they still find themselves in a similar position in the rankings in seat share (ninth out of 16) and slightly below the average (55.7 per cent for new governments), their 54.4 per cent puts them slightly above the average of new governments elected since 1921, when a multi-party system first began to implant itself on the Canadian political landscape.

New governments since 1921 have averaged a seat share of 53.5 per cent. So while that makes the Liberal government rather typical in size, the Liberals' performance does put them ahead of such first-time winners as Mackenzie King in 1921 and Stephen Harper in 2006. (Harper's seat share of 40.3 per cent during his first term in office was the smallest for a governing party.)

But though the Liberals had a middling performance in terms of overall seat share, they broke records in the increase they made between the 2011 and 2015 federal elections.

After the 2011 vote, the Liberals occupied just 11 per cent of the seats in the House of Commons. The increase in seat share experienced by the party in 2015 (43.4 points) is the largest in Canadian history, beating out the previous record-holder of Mulroney in 1984, when he increased his PCs' share by 38.3 points following Joe Clark's defeat in 1980.

Of course, this record for the Liberals is partly an indication of just how poorly they did in the 2011 election.

A modest popular vote mandate

If the 184 seats won by the Liberals stand as at least a respectable historical performance, the share of the vote captured by the party is less so.

At 39.5 per cent, that ranks the Liberals 34th out of 42, and well below the average of 45.7 per cent that other winning parties have managed. It is also below the post-1921 average of 42.9 per cent, as well as the average record of newly elected governments, whether it be since 1867 or 1921.

No first-time government has won a majority with a smaller share of the vote than Justin Trudeau's Liberals, and only Jean Chrétien's Liberals in 1997 managed the feat as a re-elected government (Chrétien won with just 38.5 per cent of the vote in that election against a divided right). It is worth noting, however, that the Conservative majority government of 2011 won just 0.1 percentage points more of the popular vote than the Liberals this year.

Is it 2019 already?

If this is how the Liberals stack up against the historical record, is there anything we can take away to tell us something about the next federal election?

New governments always experience an increase in seat share (that is what gets them into office, after all), averaging an increase of 19.4 points. Re-elected governments, however, have averaged a drop in seat share of 1.3 points. This suggests that if the Liberals are re-elected in 2019, they would need to manage 179 seats in order to beat the over/under.

But the 2019 Liberals will not be just any government looking for re-election, they will be a government looking for re-election for the first time. In that context, the record is more mixed. On average, newly elected governments experience a drop in seat share worth 7.5 percentage points in their first re-election bid. With 338 seats in the House of Commons, that would mean the Liberals dropping to around 159 seats — and into minority territory.

However, history is unlikely to repeat itself exactly, as the Liberals have promised the 2019 election will be fought under different rules.

The historical math might be an extra incentive for the government to change those rules.