It’s not much good Labor playing the blame game about the July 28 date of the five Super Saturday byelections. In fair part, it has been the architect of its own troubles.

If Bill Shorten had agreed last year to dealing with any Labor MPs who had questionable citizenship status when they nominated, this would be over. But he insisted the ALP members were all okay. They weren’t. It was a case of hubris and short-term tactics.

Now the ALP has been hit with a byelection date that means its July 26-28 national conference has to be postponed. More important, the campaigning will be strung out and so enormously expensive for Labor – which must spend whatever it takes. This will bleed its funds in the run up to a general election.

The new government regulations designed to avoid fresh dual citizenship issues have delayed things - whether excessively can be argued over.

Labor can cry partisanship and rage at Speaker Tony Smith, who sets byelection dates, the Australian Electoral Commission, which advised July 28 was the “optimal” day, and the government, which is consulted by the Speaker (as is the opposition).

But the date can’t be changed. The ALP just has to suck it up and throw itself into battle, because the stakes are very high. Four of the five seats belong to Labor. The results in two of them will be crucial for Bill Shorten’s standing and leadership.

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Moving the national conference will bring inconvenience and financial costs. But there are upsides. Pre-conference wrangling over refugee policy was already underway – policy jostling would have been a negative if the byelection date had been early July.

To be frank, Shorten would be better off if the conference could be scrapped. Whenever it is held, it will inevitably highlight internal differences. Killing it altogether, however, isn’t feasible.

The July 28 date sparked speculation about whether Malcolm Turnbull could later morph the byelections into an early election. Prime Ministerial sources say “absolutely not”.

The polls are tightening – Newspoll and Essential both have Labor’s two- party lead at a modest 51-49% - and there is a better vibe around for the government. But Turnbull needs more time and besides, after repeatedly saying the election is next year he would be marked down for going back on his word.

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Read more: Post-budget poll wrap: Labor has equal best Newspoll budget result, gains in Ipsos, but trails in Longman

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While Super Saturday has implications for Turnbull, it is Shorten who has most at risk. If the status quo holds, Turnbull can say, that’s byelections for you.

Apart from the four Labor seats, the other contest is in the South Australian electorate of Mayo, which has been held by the Centre Alliance’s Rebekha Sharkie. The long campaign will be financially hard for her; she’s up against a well-known, well-resourced Liberal candidate in Georgina Downer. But some Liberal sources say Sharkie is popular on the ground and a crossbencher in a semi-rural seat can dig in.

It is Longman in Queensland and Braddon in Tasmania, both on close margins, that are the crunch seats for Shorten (the Liberals aren’t standing in the Western Australian seats of Perth and Fremantle). Essentially, voters in these two seats will determine whether Shorten’s leadership becomes an issue.

While his position has been safe, Shorten operates against background chatter about whether, when push comes to election shove, he will get Labor over the line. So far the opinion poll evidence has suggested he will, but in Labor there’s concern about voters’ negative response to him.

He’s sensitive to the speculation, with always an eye to Anthony Albanese, the man he beat for the leadership after Labor’s 2013 loss. Albanese, with an eye to expectations, predicts Labor will hold all of its four seats on Super Saturday.

Shorten’s position was impregnable following the ALP’s strong showing at the 2016 election. It is still robust, and in the normal course there would be no possibility of change.

But “Super Saturday” has injected the abnormal, a new test in real time.

Apart from Tim Hammond’s resignation from the seat of Perth for personal reasons, the contests in the other three Labor seats are because of the citizenship crisis. In the government electorates of New England and Bennelong last year, voters weren’t censorious about MPs’ constitutional carelessness; Labor hopes the tolerance has lasted.

If Shorten lost Braddon or Longman he would be flying against history – only once (in 1920, when the Labor member had been expelled from parliament) has a government won a seat from the opposition at a federal byelection.

A defeat in one of either Braddon or Longman would be destabilising for Shorten. He’d likely hold onto his leadership, but everything would become more difficult, including managing a delayed national conference.

If Shorten lost both seats, anything could happen. Labor would be shaken to its core.

At the worst, there could be a leadership move against him, although the ALP rules would work to protect him. Under changes sponsored by Kevin Rudd, who knew a thing or two about coups, 60% of caucus must petition to open the opposition leadership during a term – then a lengthy ballot involves the rank and file as well as the caucus.

But Caucus is master of its destiny and so can vote to wind back the clock from the Rudd rule. Overturning the rule, however, would be extremely controversial, although it could not be entirely ruled out if two seats were lost.

At the very least, losing both seats would fundamentally change the political dynamics for Shorten.

Both Shorten and Turnbull have been on the campaign road for the byelections. At this early stage, neither side seems to have a fix on Longman and Braddon. The Liberals point to history. Labor remains nervous.

The Liberals polled well in Braddon at the state election. Their candidate is the former Liberal federal member for the seat, Brett Whiteley.

Last time the ALP won Longman on One Nation preferences, which it won’t get again. A recent poll was positive for the Liberal National Party, which is running a former state MP.

In each of the campaigns, local factors will be critical. But the national argument about tax will also be in play, with two competing income tax packages on display, and also the government’s tax cut for big business, from which Pauline Hanson, with Longman in mind, withdrew her support this week.

We know from history that key byelections can have big political impacts. And that’s been when there was only one on the day.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.