Heather du Plessis-Allan: Simon Bridges and Jami-Lee Ross are both finished

COMMENT: New Zealand, the House of Cards writers just called. They want to buy the script. That's how ugly this past week in politics has been.

Both sides have played dirty. Both the National Party and Jami-Lee Ross have smeared each other horribly.

Both sides are badly wounded.

Ross' future is determined. It's really up to him when it happens, but it will happen. He will eventually slink out of politics. He can't survive the wounds he's inflicted on himself. Who's going to re-elect a man untrustworthy enough to cheat on his wife multiple times, attempt to publicly name the MP he cheated with, secretly record conversations with colleagues and then release those tapes publicly?

National leader Simon Bridges' future is also determined. He will be rolled. It won't happen immediately but it will happen.

Don't be fooled by National's "nothing to see here" act. There's plenty to see. National is a party in crisis. It's been shocked and rocked by Ross setting off his political suicide vest this week.

Bridges' future will play out in stages.

Right now National is in Crisis Stage One. This is where the party acts like a cat in a corner. It defends and attacks at the same time.

The party is in full attack-Jami-Lee mode. Why do you think at least four women have suddenly come forward accusing Ross of everything from bullying to "brutal sex"?

The party is also in full defence mode. This is where MPs are told to toe the line or else. They're told who to talk to, what to say, when to smile, where to be.

Take the case of Maureen Pugh. This is the MP described by Bridges in a secret recording as "f**king useless". As soon as that tape leaked, National took over her life. They took her phone off her. A staffer answered it on her behalf. They probably drafted the tweet she sent out accepting Bridges' apology. They marched her out to tell TV cameras she was fine. They sent another MP for support. Or supervision.

They wheeled out the senior MPs Bridges slagged off. The senior MPs were also told to say it was fine. But you only needed to listen a little more carefully to hear things weren't fine at all. On radio, former Attorney-General Chris Finlayson spent far too much time describing what a hard worker Maureen Pugh is. Which is to say, he doesn't think she's "f**king useless". Which is to say, he flipped the bird at Bridges publicly. So, he's not quite as chill as National would like to pretend.

Stage Two comes next. This is the Shock stage. By this stage, the story will have died down, so the adrenaline will have worn off. National's polling will probably have dropped. The party's support will likely have taken a huge knock.

MPs at this stage will feel aggrieved about the dead rats they were forced to swallow and the cups of concrete they were told to drink. They will wonder whether it was worth sucking up whatever they were told to suck up, given that the polls still dropped.

Cue disgruntlement.

Then comes Stage Three. The Roll.

This where Bridges gets rolled. This stage only comes after a big drop in the polls. No one will roll Bridges without that. No one wants to be the person who rides the polls down. But everyone wants to be the white knight who carries them back up. So a low polling is a prerequisite.

Also, this stage only comes after a bit of time. No one wants to roll Bridges right now. It's too close to the Ross detonation. Anyone who benefits too quickly could be seen as kicking Bridges while he's wounded. That's ugly. It's better to be gifted the leadership than to snatch it from a hurt man.

Given that we're only in stage one, there's a lot more drama to come. Things will inevitably slow down, but the mutually assured destruction is almost a certainty.

• Heather du Plessis-Allan is on Newstalk ZB in Wellington, weekdays, 8.30am-noon.