TWENTY years ago, Paul Keating drew from a wildlife documentary to describe a vulnerable political leader.

Mr Keating had been fascinated by a National Geographic scene in which a large, powerful wildebeest was stalked by lions which one-by-one attacked, wounded and finally dispatched the animal.

To adapt his conclusion to late 2017: “Malcolm Turnbull is a wildebeest.”

The Prime Minister began the week strengthened by the same-sex marriage victory in the Senate, the renewed disgrace of Labor senator Sam Dastyari, and the expected by-election return of former National’s leader Barnaby Joyce.

He was only a week away from actually having a Deputy Prime Minister again.

But then came Thursday’s surprise announcement of a banking and financial sector royal commission.

Mr Turnbull’s vulnerability on the political Serengeti was exposed and the consequences could be politically fatal.

He described the royal commission decision as regrettable but necessary.

Prime ministers in charge of their back benches eliminate the regrettable before it becomes necessary. Mr Turnbull could not.

Keating would have stared down rebels, John Howard would have talked them down. Malcolm Turnbull appeared to have only a backdown.

One consequence is further challenges to his authority and political and policy management, not least by Labor which claims the royal commission could have been called 601 days earlier had the Prime Minister taken the Opposition’s advice.

That type of taunt could be expected.

More damaging is the revitalised separatism among some Nationals who want to take all the credit for the royal commission move, leaving Mr Turnbull a mere functionary of their ambitions.

In turn, this has riled Liberals who want the Nationals to accept their position as the junior partner in the Coalition.

So who else could the inquiry upset? Of course, the trade union movement.

The royal commission terms of reference appear aimed at industry superannuation funds which have significant union involvement. There will be accusations there is a political barb in this move, just as there was in the so-called Pink Batts royal commission which was launched with loud fanfare by then-Environment Minister Greg Hunt, who later neglected to tell us how the Government responded to its findings.

The saving element for Mr Turnbull, the factor keeping the pack at bay, is the absence of a likely replacement.

Tony Abbott is not on any list, Peter Dutton, Scott Morrison and Julie Bishop are mentioned, but nobody has the dominance to guarantee success.

Further, Labor has shown in painful detail what happens when sitting prime ministers are punted by MPs and not by voters.

NSW Deputy Premier and National John Barilaro on Friday told right-wing broadcaster Alan Jones that Mr Turnbull should quit by December 25 as a Christmas present to the nation. His brashness to an audience trained by Jones to be anti-Turnbull had all the sounds of a planned insult.

Mr Barilaro wasn’t just speaking for himself.

Malcolm Turnbull will see through Christmas and most probably will still be there at a general election in late 2018.

But the instability will continue, and those lions will become more determined.