The list of people who have declared they will not run for the leadership of the Conservative Party or the NDP is more illustrious than the list of contestants already in the race or mulling a bid. Could it be that some of these opt-outers already consider the 2019 federal election a lost cause?

On the Conservative side, former heirs apparent like Peter MacKay and Jason Kenney have decided they have better things to do than take over the party. Other leading figures within Stephen Harper's government, such as John Baird and James Moore, both now working in the private sector, have also said they will be sitting this one out.

Instead, a group of Conservative MPs with low name recognition have thrown their hats in the ring, while others with similarly limited profiles are expected to declare their intentions soon.

For the New Democrats, Megan Leslie, Nathan Cullen, and Alexandre Boulerice have all announced they will not be running to replace Tom Mulcair, and no one else has yet stepped forward.

Is this a coincidence, or is there a belief that the real leadership races to win will come in the run-up to the following federal election in 2023 — after the Conservatives and New Democrats have offered up some sacrificial lambs for electoral slaughter in 2019?

Though few aspirants to the job — whether now or in the future — will publicly admit such a thing, there is no doubt that it is part of the calculation.

But it isn't defeatism to believe that the odds are in favour of Justin Trudeau's Liberals being re-elected in 2019. It is the safer bet, according to past history.

One-term governments are the exception

One-term governments in Canada's history are marked by asterisks. The last one was in 1980-84, headed by Pierre Trudeau and, briefly, John Turner. But that single-term government was the result of a short interruption caused by Joe Clark's Progressive Conservative victory in 1979. Prior to that, Trudeau and Lester Pearson's Liberals had been in power since 1963.

Clark's, too, was an unusual one-term government, as his PCs had taken a smaller share of the popular vote than Trudeau's Liberals in the 1979 federal election.

Another set of asterisk-laden one-term governments was in the 1920s. Mackenzie King's Liberals, first elected in 1921, finished second in the 1925 election — but stayed on in office. King's minority government fell in 1926 and Arthur Meighen's Conservatives were sworn in for a few months, before being defeated by King in an election held later in the year. That government was then defeated in 1930 by R.B. Bennett.

Whether any of those count as one-term governments is up to interpretation. But Bennett's one-term government of 1930-35 was without any caveat — and the Great Depression may have had something to do with Bennett's defeat after one kick at the can.

In all, of the federal governments that have been formed in Canadian history less than a third could be considered single-term governments. At the provincial level, less than a fifth of governments have been given only one term in office.

That means it's reasonable to expect that Trudeau's Liberals will not be one of the rare exceptions — something to keep in mind if you are trying to decide when to make a jump at a leadership bid.

A long-term commitment...

One of the considerations cited for sitting out the NDP and Conservative leadership races is the significant commitment of time. If there is a hope of leading their party to government for at least two terms, that means a commitment of a few years on the opposition benches and another eight years in power. Add another four years to that tally caused by a second Trudeau term, and the commitment of time approaches 15 years.

On average, federal governments have been given about 2.5 terms in office and have held power for just under nine years.

That is a long time to remain in opposition for any aspiring leader. But that also assumes that the successful leadership contestant would remain in the job long enough to see the end of the Trudeau years. That is by no means a given.

... and a long-term investment

While the higher-profile candidates may be waiting for a better time, lower-profile candidates will make the case that they are a better longer-term investment for the party. Even if they don't win in 2019, the extra experience and familiarity provided by years on the opposition benches would make them strong leaders by 2023.

This might be an easier case to make for New Democrats than Conservatives. On average, NDP (and before them, CCF) leaders have led their party through 2.8 elections. Tom Mulcair's one election campaign is actually an exception — the only other one-election NDP leader was Audrey McLaughlin, who led the party to its worst showing in 1993.

Conservatives have been less keen on giving their leaders a second chance. Past Conservative leaders (including those of the Progressive Conservative, Reform and Canadian Alliance parties) who have failed to become the prime minister have only stayed in the job for an average of 1.6 elections. Those who have succeeded, on the other hand, have stayed in place for an average of 3.8 elections.

Examples of Conservative leaders who have lost their first elections and stayed on to eventually become prime minister are relatively rare. Stephen Harper was one of them, but he was the first to manage the feat since Meighen in the 1920s (Robert Borden was the only other one).

Calculating that the next leaders of the Conservative and New Democratic parties will, first, lose in 2019 and, second, be gone before 2023 is entirely sensible. But it is still a gamble.

Jack Layton took over the NDP in 2003, when the party was struggling, but stayed on for four elections and could have stayed on for more had he not passed away in 2011. Stephen Harper, who could have been an also-ran after losing in 2004, stayed in the job for four more elections and won three of them. Justin Trudeau took over a Liberal Party in 2013 that had few prospects and that no one else of stature wanted to lead.

Going now or keeping options open for going later — both require a leap of faith. So far, the heavyweights of the Conservatives and NDP seem to be going with the odds.