Well, the Russian invasion of Russia turned out to be vastly more successful than the Russian invasion of Ukraine.

After 16 months of stalemate, with Russian forces bogged down by incompetence, corruption and infighting, the Ukraine war yesterday boomeranged right back at Vladimir Putin.

The rebellion by his Wagner militia is the most significant challenge to him since he came to power 23 years ago.

And though Putin´s former ally Yevgeny Prigozhin pulled back in his advance on Moscow — allegedly to avoid bloodshed — two things now seem clear.

The first is the likelihood that this is the beginning of the end of the war in Ukraine.

Russian forces have been at a stalemate for over a year now, having failed to seize the Ukrainian capital in the opening days of the war, and proving unable to gain any significant new territory since.

By contrast, after accusing the Kremlin of deliberately bombing his own troops, Prigozhin in 24 hours managed to storm into Russia, take over at least one city and get within a few hundred miles of Moscow. Putin appears to have fled the capital.

Whatever happens now, it is impossible to see how Russia will be able to regain any momentum in Ukraine.

Since the start of the conflict, Putin has relied on mercenary groups like Wagner who report to their own commanders.

This has allowed Putin to circumvent the incompetent Russian military but also set up a problem for him.

Because when these militias had any success, the resulting glory went to the militia heads, not to Putin and his “special operation.”

The Russian position now could hardly be worse. The Ukrainian counteroffensive has already begun, and the Ukrainians are fighting an opponent bitterly divided within itself.

Prigozhin has accused Putin and his defense minister of pushing young Russian men into a meat grinder of a war, as well as of deliberately bombing Wagner positions.

He has also said Russia only went into Ukraine because of lies pushed by the top brass of the Russian military.

In such a situation, and in the midst of an apparent coup attempt, how could Russia possibly win an already unwinnable war in its neighboring country?

The second thing that is now obvious is that either Prigozhin or Putin will have to go. But whichever it is, the iron grip Putin has had on his country for almost a quarter of a century is finally loosening.

For now, it looks like it is Prigozhin who has stepped back from the brink.

But Russia will remain on the brink for the foreseeable future. Yesterday a visibly furious Putin made a video message in which he said that Prigozhin´s actions were a “betrayal” of the Russian people and a “stab in the back” of the country and its people.

There is now talk of some moving around of personnel at the top of the Russian government.

For months Prigozhin has been blasting Russian Defense Minister Sergei Shoigu and the country’s top general, Valery Gerasimov.

Some people think Prigozhin may be placated if these men were to be fired or replaced.

But it is far too late for that.

Prigozhin´s statements have not simply been a criticism of two people — any more than his brief march on Moscow was about a couple of top brass.

His statements and actions have been an attempt to overturn the whole rationale for the war, its operation, and the people who started it. It is a grab not for land but for power.

That is not a fire that Putin can put out by a bit of mere cabinet rearranging.

Putin will have to act, fast and ruthlessly.

Already his internal security service, the FSB (formerly the KGB), have said it has opened a criminal case against Prigozhin for armed mutiny, before claiming also to have dropped it.

Meanwhile, it has been reported that over the past 24 hours, the homes and former homes of members of the Wagner militia have been raided by the FSB.

All of which suggests that Prigozhin also knows that this is a fight to the death between him and Putin. One of them is going to have to go.

There will be those in the West who will be cheering Prigozhin on.

Not least because the weaker Putin is, the more likely it is that his illegal and bloody war in Ukraine might finally come to an end.

But while that would certainly be a desirable end, almost nothing else in this saga should be cheered.

Prigozhin is just as much of a thug and killer as Putin. Perhaps even more so.

What we are seeing may well be the beginning of the end of the war in Ukraine. But it is almost certainly also the beginning of the end of Vladimir Putin.

Few people will mourn that fact. But anybody with any sense of history will remember that the history of Russia is that everything can always get worse.