Gerry Brownlee says he's not surprised National did so poorly in the recent Newshub-Reid Research poll, which he called "rogue".
National fell to 25.1 percent in the July poll, well below Labour's 60.9. It was conducted in the days after the party changed its leader for the second time in two months, lost veterans Nikki Kaye and Amy Adams, and had an MP resign in disgrace over alleged sexual text messages.
"It was hot on the heels of those three incidents... all of which had everybody in shock, including us," Brownlee, National deputy leader, told Magic Talk's Road to the Election on Sunday.
"It's not surprising there was a question mark over our ability to lead a Government."
Brownlee called that poll "rogue". National fared slightly better in a later poll by Colmar Brunton.
"Our own polling is much closer to Stuff's which came out at the same time," he said, admitting the Stuff poll was not a scientific poll.
Asked what numbers their internal polling is suggesting, Brownlee said "around about the 40 percent mark".
He said he no longer trusts polls.
"No one would have predicted on polls that Trump would win, no one predicted that Boris Johnson would win on the polls, and certainly no one thought that Scott Morrison would return with any kind of a majority in Australia, because of the polls."
But he was happy to hear about NZ First's struggles in the polls in Northland, with Shane Jones well behind National's Matt King.
"That Northland poll... is a clear indication of where NZ First sits. They've got a very difficult road to get back into Parliament."
National has previously ruled out working with NZ First, but Brownlee appeared to open the door slightly, saying "no one is totally fixed to any idea forever."
The election is six weeks away.