That’s not hypocrisy. North Korea is not Iraq - it really does have nuclear weapons, it fires artillery at neighbouring countries and regularly threatens to murder us. And Gary Johnson’s plan is not Bush’s plan - he wants to work with China to bring the Kim regime to an end without a war, instead of invading a hostile nation under false pretenses and without the blessing of the United Nations and assuming they’ll welcome us with open arms.
And the second it tried to use them, it would become either a Chinese annex or a parking lot (or both). No one takes Un’s threats seriously except his neighbors. He’s a stuffed shirt talking himself up to impress his party.
Bottom line is Johnson’s policy is pure fantasy. There are only two ways to take down N. Korea: economically choking them off completely or invasion.
Regime change is regime change. And assuming that Kim Jong Un would step down willingly, without a fight, borders on insanity. It sounds like something Trump would throw out in the middle of one of his rambling speeches. As you mention, they have nukes, and there is nothing to indicate they would be hesitant to use them if China or the US tried removing Un.