Should National pull a Jacinda Ardern and leave it to the last minute to roll Simon Bridges?

Simon Bridges' job is probably safe - at least up until six weeks before the next election, according to political commentator Chris Trotter.

The National leader is struggling to win over voters, registering at only 7 percent for preferred Prime Minister in the latest Colmar-Brunton poll. That's in stark contrast to his party however, which is as strong as it's ever been under his leadership - 46 percent.

The left-leaning Mr Trotter says it's likely Mr Bridges won't be rolled anytime soon - but shouldn't assume he'll lead National into the 2020 election.

"If you're going to change your leader, the historical precedent now has been set with Jacinda - that is you spring it on people."

Jacinda Ardern took the reins for Labour on August 1, 2017, only seven weeks before the 2017 election. The polls reacted immediately, and by October she was Prime Minister

Before she became Labour leader, Ms Ardern was already on 8.7 percent as preferred Prime Minister in the previous Newshub-Reid Research poll. Then-leader Andrew Little was on only 7.1.

Both are ahead of where Mr Bridges appears to be now.

Trish Sherson and Chris Trotter.
Trish Sherson and Chris Trotter. Photo credit: The AM Show

Political commentator and former ACT press secretary Trish Sherson - appearing alongside Mr Trotter on The AM Show - wasn't so sure Mr Bridges would be toast.

"If your party vote is on 46 percent, you'd have to be a turkey voting for an early Christmas if you moved at that point."

Mr Bridges himself has sought to put the focus on the party vote.

"Under my leadership what really matters is the party vote, and that's going up," he pointed out to AM Show host Duncan Garner on Monday.

Mr Trotter said the high party vote numbers were the only thing keeping Mr Bridges off the Christmas menu.

"If those numbers go down appreciably into the 30s - around 35, 36 - then he's in trouble."

Funnily enough, about 36 percent was enough to get Labour into Parliament - but National's only reliable ally is the single-seat ACT Party, and not even 47 percent was enough to win them power at the last election.