If federal parliament wasn’t already at a low ebb in terms of credibility with the electorate before Tuesday, courtesy of the citizenship debacle, Stephen Parry made sure it got there with behaviour so ridiculous it left even his colleagues bewildered and the Prime Minister fuming. Parry, informed by the Home Office that he had British citizenship, resigned from politics yesterday afternoon, his apparent plot to be rescued from embarrassment by the High Court having been dashed last Friday.

Turnbull made his anger clear in his public remarks in Israel: “I’m disappointed that Senator Parry didn’t make public this issue, this issue some time ago, quite some time ago … he should have reported it much earlier.” Damningly, he said, “I learnt about it probably about the same time you did on Tuesday, yesterday.”

That was the big political sin of the now Mr Parry. No matter how egregiously you screw up, you never leave your leader to be surprised like that.

Parry’s departure, naturally, was the signal for a brawl between the Liberals and the Nationals over who got the choice gig of President. John Williams, who has displayed more dignity, consistency and commitment as senator than most of his colleagues, has put his hand up. But so too has Queensland LNP senator Ian Macdonald.

If the government doesn’t want to reduce the credibility of politics even further, it will make clear to Macdonald he won’t have the gig. Macdonald is partisan and self-centred: he spat the dummy when Tony Abbott didn’t give him a frontbench spot in 2013, he lashed out at the government when it moved to cut back post-political travel entitlements. But he’s most famous for being by far the worst committee chair in the Senate. While every other Coalition committee chair acts with decorum and a degree of non-partisanship, Macdonald’s chairing of the Legal and Constitutional Affairs committee regularly produces major brawls.

Earlier this year, he tried to throw a senator off a committee and was then humiliated when he was forced to admit he didn’t have the power. Worse, even his Coalition colleagues plainly don’t like the way he carries on. His chairing of Legal and Constitutional Affairs is so antagonistic he even ended up upbraiding George Brandis during hearings last week. And he barged into Linda Reynolds’ Education and Employment Committee to try to instruct her on how it should be run while Michaelia Cash was being grilled by Labor last week, forcing her to tell him to back off.

Macdonald shouldn’t even be in the Senate. The idea of him running it would reduce it to a laughing stock.