Former prime minister John Howard has told Liberal voters in Wentworth they risk "robbing" the Morrison government of its parliamentary majority if they don't vote for the party in Saturday's by-election.
"If enough people decide to register a protest vote then the seat could go to an independent and that will rob the Morrison government of its working majority and make the remaining months of this term of office very difficult," the former Liberal leader said when campaigning alongside candidate Dave Sharma in Double Bay.
It's been reported senior Liberals wanted former Wentworth MP and ex-PM Malcolm Turnbull to come out strongly in support of Mr Sharma but, in his absence, the party today brought out Mr Howard.
"There's no such thing in modern politics as an unlosable seat," he told reporters.
"This seat may have been held by the Liberal Party or its predecessors since federation but every election and every by-election is different."
Mr Howard acknowledged people were "grumpy" about the Liberal Party knifing Mr Turnbull as leader in August.
"A lot of people here are sad that he's not any longer the member and prime minister but others will take a view projecting forward," he said.
Earlier he admitted to 9NEWS winning Wentworth "is going to be very tough".
Mr Turnbull did still enter the Wentworth by-election fray, but not in the way the Liberals envisioned.
The former prime minister liked a tweet posted by a supporter of Kerryn Phelps, saying “hoping for a strong independent win on Saturday”.
Robert Fairhead put up a photo from a pre-poll booth, standing beside a poster asking “Where’s Malcolm?”.
Mr Turnbull's account has since un-liked the tweet.
The former prime minister is reported to have left New York, but won’t be home before Saturday’s crucial poll and has mostly stayed out of the campaign.
The ex-member’s son Alex has also been active on social media, urging Liberal voters to desert the party after his father’s political assassination.
Turnbull senior did, very early on, endorse Liberal candidate, Dave Sharma, after backing his pre-selection.
Meanwhile, the Liberals have strongly denied any involvement in an ugly smear campaign against Independent candidate, Kerry Phelps, claiming she has HIV and is withdrawing from the by-election.
An e-mail from a fake account began circulating yesterday, just days out from the vote that could reduce the coalition to minority government.
Appearing together on the Today Show, the Liberals' Dave Sharma and Independent Dr Phelps, dismissed the smear as disgusting.
Mr Sharma, who's trailing the former AMA president in the polls, said he was "shocked and appalled" by the e-mail, saying it was "vile and despicable".
"This has no place in any campaign," Mr Sharma said.
"It's disgusting."
Both said it also stigmatised HIV and those who have it.
Dr Phelps said the e-mails were "hurtful" and "terrible".
"They're hurtful not just to me, but a lot of other people," she said.
"I was warned there could be dirty tricks.
"The fact is that they claim - they claim falsely - that I'm dropping out of the race because I have been diagnosed with a serious illness, I think, also highlights the fact while we think that the stigma around HIV has gone, it clearly hasn't."
Prime Minister Scott Morrison described the Phelps smear as "disgraceful and outrageous" and said he'd be "horrified" if the Liberals were involved.
"This is the ugly side of Australian politics and it has no place," he said.
Mr Howard joined Mr Sharma and Mr Morrison in condemning the email.
"I think it's disgusting and I utterly repudiate it. It deserves our contempt," he said.
As to former prime minister Mr Turnbull's role in the campaign, Mr Morrison said his predecessor had tweeted "in favour" of Mr Sharma and he'd been his "hand-picked candidate".
The Australian has published what it reported was internal Liberal polling showing Ms Phelps leading the Mr Sharma, 55 to 45, after preferences.
A loss would plunge the Coalition into minority government, and be one of the biggest by-election losses in history, with the Liberals holding the blue-ribbon seat with an 18 percent margin.
With AAP.