Well, Russia has finally switched tactics so that they are NOT overstretching their supply-lines, and my opinion is that if the Russian government had done this, to begin with, they would have already dominated the eastern half of the country, by now, and they also would have probably gotten control over their entire Black Sea coast. Kyiv most likely would not have stood until the end of the year.
However, it is too little, too late. The economic effects of global sanctions have had time to start taking their toll, and in the long-run, they are going to run out of their more expensive weapons. They are not really going to be able to continue minting new tanks fast enough to keep up with the rate at which Ukraine has been destroying them, whereas Ukraine still has enough international sympathy that they have new equipment rolling in by the day. Ukraine still has access to the Black Sea through Odessa.
Furthermore, the frustration of Russian troops over their early failures led to early humanitarian disasters that have entrenched an intense partisan resistance, especially in the southeastern parts of Ukraine. The partisan resistance probably would not have been as fierce without the early failures of the Russian invasion, but the consequences of leaving your troops underfed, undersupplied, and terrified of an intensely hostile population is that they become angry, they become hungry, and they become desperate, which leads to the slaughter of civilians. You cannot really undo that, and the family, neighbors, and countrymen of those people are ghosts that come back to haunt you. Russia has thereby created a problem that they otherwise might not have had to such an extreme degree. Where a partisan resistance would have had little effect in a situation like they had in Crimea, which they quickly dominated with little loss of life, thereby making such a resistance unpopular and all but impossible to build support for, they have ruined the possibility of any such scenario by an excess of ambition.
Furthermore, they seriously screwed up with Mariupol. Their "kill so many of them that the rest of them are paralyzed with fear" strategy has only hardened the international community against Russia and thereby led to a tightening of sanctions. The fact that their jumping jacks in the region are bragging as if Mariupol were a glowing success that they were turning to a quick profit, Mariupol was really a failure. By flatting the city, they have not just denied that city to Ukraine, but they have denied it to themselves. Those resources that they destroyed are resources that they could have used. The civilians that they have rendered starving and angry are civilians that they could have otherwise courted at least for complacency if not for active support. I suppose the idea behind their strategy in Mariupol was to break the spirit of the region, but just to the west of the city is a center of partisan warfare, already discussed, that will ultimately make the lives of Russian occupiers as much of a living Hell as Vietnam was for the Americans. You just don't murder thousands of people and expect their survivors to do anything else in the world besides make your life so miserable as to be not even worth living.
Ultimately, Russia made the same mistake, by stretching their supply-lines too far, that Napoleon made during his invasion of Russia. While Napoleon was indeed able to win a few relatively petty victories, that disastrous campaign really was a turning point in the war that ultimately led to the defeat of Napoleon. Ultimately, it was the same tale. Napoleon marched into Russia with pride, confidence, and swagger, and he had the happy expectation that the "liberated" (read: conquered) peasants would throw flowers at his feet as he triumphantly marched into a suddenly pro-France Moscow and planted the Tricolor to the tune of a happy fanfare. The heart of his mistake was ultimately that you cannot realistically expect your soldiers to behave well if you leave them starving, and that is final. The first instance of rape, plunder, or mass murder is the beginning of your defeat.
While Napoleon might have had a few relatively minor victories later, his fate was really sealed from the moment that he assumed that hubris would not have consequences. Even if he had not made any further mistakes, it would have happened eventually because the world had turned against him where the world had previously been divided or, at times, sympathetic. His empire was doomed.
Only a fool would bet on Putin, at this point.
www.newsweek.com
