The Russian soldier was angry. His brigade had fought for weeks. Half of them were injured or dead. So, in the middle of another battle, he repositioned his tank and ran over his commanderIn total, seven Russian generals and at least 15 senior Russian commanders have been killed in Ukraine in just one month of war. . 

Reports about Colonel Yuri Medvedev's condition are unclear. Some say he died. Others say he was brought to a hospital with serious leg injuries. 

One thing is certain: Vladimir Putin's war in Ukraine is not going according to plan. "It increasingly looks like Putin has massively misjudged the situation,"  GCHQThe Government Communications Headquarters is a British intelligence and security organisation.  director Jeremy Fleming said in a rare speech. 

"We've seen Russian soldiers - short of weapons and morale - refusing to carry out orders, sabotaging their own equipment and even accidentally shooting down their own aircraft." 

At least 15,000 Russian troops are thought to have died. Others have begged for food, abandoned their vehicles and defected to the Ukrainian army. 

US intelligence believes military leaders are too scared to tell the Russian president just how badly the war is. 

Historians say there are two main ways authoritarians fall: military coups or popular uprisings. "Before the war, the risk from either of those threats was close to zero," argues academic Brian TaylorTaylor is the author of The Code of Putinism. . "And now the risk in both of those respects is certainly higher." 

Military bosses, in fear of being blamed for losses, could calculate that the best way to protect themselves is to depose Putin. Ordinary citizens, fed up with oppression, economic sanctionsEconomic measures designed to punish a country, for instance by excluding it from trade. and dying soldiers, could overthrow their government. 

Russian experts insist neither is likely. Putin has spent 20 years preparing for dissent - and taking steps to ensure it is nearly impossible. 

OligarchsAfter the collapse of the Soviet Union, most of the country's economy fell into the hands of corrupt businessmen who became known as oligarchs. Putin cemented his early popularity by cracking down on these oligarchs, although he has since created a new oligarchy that is loyal to him. rely on Putin for their wealth. Russia's military is filled with spies.

Protesters face challenges. Their leaders are imprisoned or killed. Independent media is shut down. 

The support protesters enjoy is limited, despite sanctions. "Russians are famously stoical," points out journalist Owen Matthews. Independent polling shows Putin's approval rating in Russia has risen, from 71% in February to 83% today. 

Most agree with Matthews that "Putin's mask of invincibility has cracked". The question of whether it will fall off entirely will affect the people of Russia - and even the whole world - for decades to come. 

Yes:  Every military loss in Ukraine makes the possibility of a revolt in Russia more likely. Generals will take action to prevent a costly war. And the Russian people will not put up with hardship for long.

No: Most academics agree that Putin's grip on power is too strong to fail. Military bosses rarely undertake coups without a guarantee of success. And anyway, there is no potential replacement to step in.

Or... It took 13 years for the Russo-Japanese war to topple Tsar Nicholas II. Brezhnev's invasion of Afghanistan came 12 years before the USSR's end. Putin may be wounded, but his fall will not be quick.