Labor may have to fight as many as four more byelections in early 2018, after John Alexander's victory in the crucial Bennelong byelection restored Malcolm Turnbull's one-seat majority.
The victory in Bennelong also makes it more likely Mr Turnbull will reshuffle his front bench later this week, though after the release of the mid-year budget update on Monday that will show the federal deficit will be $23 billion lower than forecast by 2021.
Lower house MP David Feeney was referred to the High Court over his possible dual UK-Australian citizenship earlier this month. Now that the government has its one-seat majority in Parliament again, it has the numbers to refer Labor MPs Justine Keay, Susan Lamb and Josh Wilson to the court.
NXT MP Rebekha Sharkie is in a similar situation, which would mean a total of five referrals could be made to the court. If the court finds the MPs were not eligible to be elected because of their dual citizenship, byelections would then be held.
Three Labor and NXT MPs had not received confirmation of their renunciation of their UK citizenship when nominations closed for the 2016 election, though the ALP has argued their members took all "reasonable steps" to renounce UK citizenship and therefore should be in the clear.
The victory in Bennelong, which follows a byelection win for deputy Prime Minister Barnaby Joyce two weeks ago, the successful legalisation of same-sex marriage and the recent resignation of Labor senator Sam Dastyari, caps a strong end to what has been a mostly difficult year for Mr Turnbull.
Conversely, Opposition Leader Bill Shorten will start 2018 on the back foot if Labor has to fight to hold four of its seats; Mr Feeney's seat of Batman, in Melbourne, is at particular risk of going to the Greens, especially as the Coalition is unlikely to stand a candidate.
A senior Labor MP said the relatively small swing of about five per cent to Labor's Kristina Keneally was "a terrible result, we poured a lot of resources into it and it's an ordinary outcome".
"Bill was a big negative in Bennelong but he wouldn't stay away."
On Sunday, Mr Turnbull strongly hinted the citizenship saga, which has seen a swag of MPs and senators disqualified and which began in July, will drag on into the new year.???
"The Labor Party at this stage, even though they have two people in the House of Representatives who are UK citizens now, neither of them have stepped down, and the risk of by-elections next year falls clearly on the Labor side."
The government's chief parliamentary tactician, Christopher Pyne, went further and confirmed the referrals were on the cards.
"Our first preference is for Bill Shorten to do the right thing and refer his own MPs. In the absence of that, we won't be complicit in a Shorten protection racket. If necessary, we will refer any MP with a serious case to answer," he told Fairfax Media.
"The MPs for Longman [Ms Lamb], Braddon [Ms Keay] and Fremantle [Mr Wilson] have all admitted they were British citizens when nominations closed for the 2016 election. They have a prima facie case to answer, as does the MP for Mayo [Ms Sharkie]."
In the wake of the Bennelong loss, Labor front bencher Tony Burke said there was "no doubt" the resignation of senator Sam Dastyari had hurt Labor in the Bennelong byelection.
In addition, Mr Burke said the lesson from the byelection was that "the next election will be hard" but that if the swing Labor won in the seat was repeated across the country, "we wouldn't have won Bennelong but we may well have won government".
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However, he said, "there are enough people willing to change their votes that with the right work and the right policies, we can get there".
As counting in Bennelong continued on Sunday, with 79.5 per cent of the vote counted Mr Alexander had won 54.78 per cent of the two-party preferred vote, and Labor's star candidate Ms Keneally claimed 45.22 per cent.
That represents a swing of 4.94 per cent to Ms Keneally, a result that is broadly in line with swings that typically occur in byelections in government seats.
In the cabinet reshuffle, the Prime Minister needs to make room for newly-elected Nationals deputy leader Bridget McKenzie in his cabinet, former Special Minister of State Scott Ryan needs to be replaced, while there is a question mark over whether Industry Minister Arthur Sinodinos, who is battling cancer and currently on leave, will continue in his role.
In addition, Immigration Minister Peter Dutton's new department of Home Affairs is expected to begin operating this week, and some MPs expect George Brandis to step down and take up the post of High Commissioner in London - though the Attorney-General has indicated he wants to continue in his job.
