If you wanted a sense of the divide between right-wing senator Alex Antic and some of his Liberal colleagues, you only have to look at events in parliament this week.
Senator Antic had introduced a bill to allow parents to still receive their family tax benefit if they, on the grounds of "personal, philosophical, religious or medical belief", objected to their child being vaccinated.
Senator Antic's bill sat on the notice paper for nearly a year, indicating it did not have many friends in Canberra.
Thirty-four senators voted it down, including Liberal frontbencher Anne Ruston, who defended the former Coalition government's policy and raised concern about a recent rise in whooping cough and measles cases in Australia.
"We are already seeing hospitals operating beyond their capacity," Senator Ruston said, citing advice from the Australian Medical Association.
Senator Antic was the only Coalition member to vote for the bill.
Labor has already signalled its intent to link Senator Antic's views with the Liberal Party as a whole.
Labor senator Murray Watt said on Wednesday.
"Senator Antic has not only taken over the Liberal Party in South Australia, but is on track to become its president in South Australia."
His supporters are framing Saturday's presidency ballot as a referendum on whether the SA Liberal Party remains a conservative party.
At the last poll taken in August, the SA Liberals' primary vote was still eight points behind One Nation's.
If Senator Antic is elected president, attention will turn to the Liberal Party's policy direction.