Voting to elect a new Scottish leader after Nicola Sturgeon's surprise resignation opened on Monday, with all three candidates pledging to reinvigorate her spluttering push to win independence.
Sturgeon's independence drive hit trouble after the UK government blocked her plans to hold a fresh referendum on the issue.
The vote is the Scottish National Party's first full leadership battle since 2004.
Sturgeon, who quit last month as both SNP leader and Scottish First Minister, had also become embroiled in controversy over her handling of a transgender rights row.
The leadership contenders include two women, one a devout Christian opposed to same-sex marriage, and a Muslim man.
Rising star and current finance minister Kate Forbes, 32, sparked controversy after she said she would have voted against same-sex marriage had she been a member of the Scottish parliament when the reform passed in 2014.
Forbes is a member of the Free Church of Scotland, Scotland's second-largest denomination, which opposes same-sex marriage and abortion.
Health Minister Humza Yousaf, 37, has won the backing of Sturgeon allies. He is the first non-white and Muslim cabinet member of the Scottish government.
The third candidate Ash Regan, a 38-year-old former minister, has pledged to restore unity to the party.
'Brave hearts'
In a debate on Thursday, Yousaf questioned whether Forbes' personal convictions put other people's rights at risk.
People want a first minister who does "not believe that they are morally inferior" and who would "protect" and "advance" their rights, he said.
"I'm the only candidate that has unequivocally said they will protect everybody," he added.
Forbes has defended her views as a matter of personal conscience but they have left her out of tune with the SNP's centre-left base.
Despite this, an Ipsos poll of all voters last week put her ahead at 32 per cent, with Yousaf at 24 per cent and Regan at eight per cent.
But Yousaf is widely seen as the preferred candidate for SNP voters.
In last week's debate, Forbes questioned whether he had the mettle to take on the UK government over its refusal to grant permission for another independence referendum.
She touted herself as the only candidate to have gone head-to-head with British Prime Minister Rishi Sunak "and won".
Regan meanwhile, claimed she alone had a credible plan to build support for independence and panned her rivals' approach as "wishy-washy".
"This is the time for brave hearts, not faint hearts," she said.
Backlash
Sturgeon has been party leader and Scotland's first minister since 2014.
But she faced a huge backlash after pushing through legislation allowing anyone over 16 to change their gender without a medical diagnosis.
The law would have allowed one rapist - who switched from male to female after being convicted - to serve a prison sentence in a women-only facility.
After uproar over the rapist's case, the UK government used an unprecedented veto to block the SNP's proposed law.
On independence, after losing one vote in 2014, the SNP has been agitating for a second referendum.
It has argued that the UK-wide Brexit referendum of 2016, which led to the United Kingdom leaving the European Union, should allow for a fresh consultation of Scottish opinion.
But the UK government has rejected that argument, and Britain's Supreme Court in November sided with London, leaving the SNP with no obvious course to achieve independence at the ballot box.
The leadership ballot opened at noon on Monday with the new leader set to be announced on March 27.