If the Coalition manages to win the looming Eden-Monaro byelection it will have pulled off a very rare political feat.

Only once in Australian political history has a federal government managed to unseat an opposition candidate at a byelection, when the sitting Nationalist government won the seat of Kalgoorlie from Labor in 1920 after the sitting MP was expelled from parliament.

That background was clearly on Scott Morrison's mind when he said on Wednesday that it would be "a rather extraordinary outcome" if the Liberal Party were to win the seat.

"It would be a one-in-100 year event for a government in those circumstances if they were to take a seat from the opposition," he said, adding his expectations were "conditioned by history".

It was shrewd move to claim underdog status and put the heat on Labor leader Anthony Albanese.

After all, the seat is Labor's to lose.

Retiring MP Mike Kelly has been a popular member, claiming the seat back for Labor in 2016 and successfully defending it last year by a slender 1.6 per cent margin - in the process breaking Eden-Monaro's reputation as a bellweather seat that is held by the party that wins government.

Despite his strong personal standing, Dr Kelly suffered a 2.1 per cent swing against him in two party-preferred terms in 2019. In the end, there were just 1685 votes in it.

With Mr Morrison riding high in the polls on the back of the government's response to the COVID-19 emergency, there are reasons to think the government could prevail.

According to a Newspoll conducted late last week, 68 per cent think he is doing a good job and his net approval rating of +40 is the best for a prime minister since Kevin Rudd at the height of the global financial crisis in October 2009.

Similarly, an Essential survey found 70 per cent approve of the government's pandemic response.

But the trick will be to translate Mr Morrison's high rate of approval into on-the-ground support for whoever gets selected as the Liberal Party and Nationals' candidates, which may not be straight forward.

For one thing, Newspoll found that although the PM's personal rating was high, overall support for the major parties was split 50-50 - a sign that although Labor and Green supporters approved Mr Morrison's handling of the crisis, they remained distrustful of the government.

Liberal and Nationals candidates could also face some challenging local issues, including the recovery from summer's disastrous bushfires and anger and distrust arising from the sports rorts scandal.

Large parts of the electorate were hit hard by the bushfires, which decimated small communities like Cobargo.

The Prime Minister's tone deaf response in the early stages of the disaster and complaints about delays in receiving assistance could weigh against the Liberal candidate, as might the sports rorts fallout in parts of the electorate.

There is also the risk that if the Liberal and National parties both run candidates the conservative vote gets split.

But Inside Story election watcher Peter Brent thinks it is just as plausible that if both government parties run candidates it will increase the overall conservative vote, boosting the flow of preferences to the Liberal candidate.

Liberal optimism might be bolstered by memories of the 2014 Griffith byelection brought on by the resignation of Kevin Rudd. In that poll the Liberal candidate managed to win a 1.25 per cent swing toward the party, coming reasonably close to snatching the safe Labor seat.

In that poll, a strong local candidate pushed Labor hard. Mr Brent said a high-profile pick such as New South Wales transport minister Andrew Constance could help put the Coalition in a winning position.

The person with most at stake in the byelection is probably Mr Albanese. If there is a big swing against Labor, it could fuel leadership unrest in a scenario similar to that experienced by Malcolm Turnbull when there was a sharp 3.6 per cent swing against the Liberals in the Longman byelection in 2018.

If the Liberals do manage to win back Eden-Monaro, it will lift Coalition numbers in the House of Representatives to 78 seats, giving it a two-vote buffer over the combined Labor, Greens and crossbench vote.

Winning the byelection itself would boost Mr Morrison's grip on his party and the extra MP would give him more space to stare down rebels and malcontents within government ranks.