In a Facebook Live on the Newshub page on Sunday afternoon, National Party leader Bill English said Jacinda Ardern must face constant embarrassment from deputy Labour leader Kelvin Davis.
"I have a deputy who I'm happy to have out in the public. For the leader of Labour Party, she has a deputy who embarrasses her every time he puts his head up," he told host Ryan Bridge.
"He says stuff that's unpredictable or wrong, and is always changing position."
Mr English said he had a far more "effective" deputy in Paula Bennett, who "is an experienced campaigner, great at working with the public and a good minister".
Ms Bennett faced widespread condemnation earlier this month after she commented that serious criminals have "fewer human rights than others".
Asked if she believed criminals had human rights, Ms Bennett said "some have fewer human rights than others when they are creating a string of victims behind them".
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Mr Bridge questioned Mr English on the viewpoint, asking: "What about the human rights thing?"
"Well, she was expressing a view, in the wrong language," said Mr English. "But I think the general point there is the team. I've got a team that's strong and cohesive, and Jacinda Ardern, whatever her capability, isn't backed by a team that's making it easy for her."