When you work in politics, there is a particular feeling that sometimes comes over you. It’s highly unpleasant, and it is brought on by a very specific situation. It arrives when, somehow, you have managed to travel so far along a certain road that by the time you realise it was indubitably the wrong one to take, there is no going back. You wish you could retrace your steps, but that option passed by long ago. Ahead of you lies a T-junction, and the thing about the two directions you now have to choose between is this: they both lead to hell.

Malcolm Turnbull no doubt experienced that sensation this morning, or perhaps in the dying hours of last night, as it became clear that he would have to agree to a banking royal commission, an option he has disparaged for the past 18 months. It is obvious that the prime minister was determined, until the last moment, to resist. Phillip Coorey reported [$] that rogue Nationals MP Llew O’Brien had been warned of the rising prospect of losing government, and that Senator Barry O’Sullivan, who has been leading the Nationals’ push for the inquiry, was urged by the PM to hold off while the government tried to imagine “an alternative which is neither a royal commission or a commission of inquiry”.

Pretty clearly, those efforts failed. Turnbull, choosing between two horrible options – the humiliation of utter retreat or losing a vote on policy on the floor of the parliament – chose the slightly less horrible. The banks sent a remarkable letter to the treasurer this morning, asking for an inquiry into their own actions, in order to “put an end to the uncertainty and restore trust, respect and confidence”. These were also the reasons the PM and the treasurer, Scott Morrison, gave in their press conference, and you can, in fact, extract a grain of truth from those words, but only by breezing past the more important truth they obscure. The government was ordering a royal commission to “put an end to the uncertainty” because the prime minister had proved unable to end the uncertainty himself.

To be fair, both Morrison and Turnbull effectively admitted this, by describing the decision as “regrettable but necessary”. It was, said the treasurer, the result of the “nature of political events”. This was obviously true, and is the type of admission you don’t often get from politicians these days. That said, I am certain the two men would have denied the political reality entirely if they could have got away with it. The fact they did not believe they could tells you something about the depth of the hole into which they have stumbled.

The rest of the press conference was filled with spin. As far as humiliating backdowns go, the two men did not do too badly. The reasons they gave were not complete negations of the truth; instead, they offered mitigating factors, little tidbits from serious people like the head of the Reserve Bank. But really none of this mattered. Everybody knew the score, and everything the politicians said was merely filler for the brutal editorialising that was about to begin.

This was in fact the second time in two weeks that Turnbull would have felt that awful feeling. Both involved attempts to avoid losing a vote on the royal commission – the last was the prime minister’s decision to delay parliament. That decision was widely criticised, but – exactly like today – there was a deathly logic to it. The really sad thing for the prime minister is that today’s decision means last week’s was not necessary.

Given that the PM has been forced to choose between terrible paths, can he really be blamed?

The answer is yes. There are two ways in which he erred, and they both stem from the same character flaw.

The first came in April last year, when the prime minister sharply attacked the banks. Headlines were dominated by violent verbs: “slams”, “smacks”, “lashes”. And the next day Bill Shorten waltzed in and took ownership of the issue by calling for a royal commission to be considered. In other words, Turnbull did what he did too often early in his prime ministership: expressed sentiments he could not, or would not, back up.

The problem is that he is still doing it.

Dennis Shanahan is right today in saying [$] that Turnbull could have prepared the ground for this shift. Why was the PM so firm last week in telling Karl Stefanovic that “there is not going to be a banking royal commission”? Why was he clear in arguing against an inquiry 48 hours before his backflip, as Labor has today delighted in pointing out? Asked by Laura Tingle what had changed in the last week, Turnbull delivered the only line that will outlive today: “Government policy remains the same until it is changed.” Technically accurate, perhaps, but not really how politics works.

All this gets even worse when you consider that, without banking mucking things up, today would have been a highly successful day for the government. Yesterday morning, Labor senator Sam Dastyari was in trouble over a report that he had issued counter-surveillance advice to a Chinese donor. Last night, audio emerged that conflicted with an earlier account Dastyari had given of a press conference in which he had contradicted Labor policy on the South China Sea. After that, Bill Shorten called Dastyari and told him to stand down from his position as deputy senate whip.

There is no question this is a huge scalp for the government. It is also the second time Dastyari has been sacked in 15 months. “Dasha” is one of the most well-known Labor figures, and has a talent for attracting media attention. The double blow of these stories is severe, and it is impossible to see him returning to Labor’s frontbench before the next election. The Coalition is unlikely to let voters forget his troubling behaviour, either; even today Turnbull was saying he should be forced to resign from the senate. (Shorten does not have the power to do so, though he could expel him from the ALP. There is no sign this will happen.)

On a day without a massive prime ministerial reversal the Dastyari story would have dominated bulletins. But sentences like that can be written about so many days under this government. “The government had a win today, but it was overshadowed by X.” Often, this is the fault of troublemaking backbenchers. Sometimes, Turnbull is to blame. Today was an impressive collaboration by both. Increasingly, though, where the fault lies does not matter. The government has travelled a long way down a road that is clearly taking it in the wrong direction; and increasingly it seems as though there are no good options left.