A refusal to support the territory's right to legislate on voluntary assisted dying was also responsible for the potential loss of the Liberals' ACT Senate seat, both Kate Carnell and Gary Humphries have said.

Senator Zed Seselja is facing a historic upset, with David Pocock well placed to take the ACT's second Senate spot.

If Mr Pocock succeeds it would be the first time in the territory's history where the Liberal Party does not hold one of the two seats. Senator Seselja was ahead in first preference votes with 44.6 per cent of the ballots counted on Monday. He had received 23.6 per cent of the vote, and Mr Pocock had received 21.9 per cent.

But Senator Seselja is still well short of a quota, and preference flows from the Greens and independent candidate Kim Rubenstein are likely to favour Mr Pocock.

Ms Carnell, who was the ACT chief minister from 1995 to 2000, said Senator Seselja had lost the votes of "small l" liberals due to his consistent approach of taking a conservative right-wing party view.

She said he had left the playing field right open and Mr Pocock had ran right into the field. Ms Carnell said the Liberal branches needed to come back to being moderate for both the sake of the party and for Ms Lee.

"It must come back, the great problem for the party and for that matter, Elizabeth, has been that the control of the party has been with the right, the conservative right, the people who surround Zed and it's just not what Canberra looks like," she said.

But it was a refusal to support a repeal of the Andrews Bill where Ms Carnell said Senator Seselja had lost votes.

"[Zed] was fundamentally saying the ACT Assembly was too incompetent to have the same powers as other states, [it] was just a step too far," she said.

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This was a view echoed by Mr Humphries, who served as chief minister from 2000 to 2001 and was also an ACT Liberal senator from 2003 to 2013 before he was ousted in a challenge from Senator Seselja.

"In the ACT's case there were undoubtedly a large cohort of traditional Liberal voters who were hived off from the Liberal heartland because they were appalled to think they were not represented in the Senate by somebody who would stand up for their rights as territorians," he said.

Mr Humphries said the potential loss of the Senate seat, followed by the ACT election loss in 2020, showed the local party need to rethink its platform.

"Our capacity to sort of speak for the people of the ACT when we have been so solidly defeated in two successive elections like this is in doubt, and we have to rethink our position very carefully," he said

"It absolutely spells the need for the ACT party to carefully calibrate its positions with the values of Canberrans. We have to think like the rest of Canberra and vote like the rest of Canberra."

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