This, from today's Economist newsletter, seems well expressed:
"Time is not on Mr Putin’s side. The reservists he is calling up do not need to be taught to shoot straight, but they need training to deal with new kit and local conditions. If deployed too soon, they will die in droves. They could be slotted into existing, depleted units to restore their strength. That would make it easier for Russia to defend its lines, though probably not to mount new offensives. It does not have enough weapons for a larger invasion force, not least because so many of its soldiers abandoned their guns and tanks when they fled recent Ukrainian advances. Realistically, it will be months before Mr Putin’s “partial mobilisation” makes a big difference in the field.
That gives Ukraine a window of opportunity. Its Western backers should step up the supply of arms, including longer-range missiles. The best nato weapons must not be used to attack Russia itself, but the parts of Ukraine that Russia is about to annex illegally should not be off-limits. The West should also train more Ukrainian soldiers. The country has plenty of highly motivated would-be defenders, but so far only Britain is offering basic training to large numbers. Other nato members should immediately pitch in, perhaps dividing the labour so that one ally focuses on air defence, another on artillery and so forth. The more of its land Ukraine can claw back before Russian reinforcements arrive, the stronger its position will be.
When Mr Putin invaded Ukraine, he thought it would fold. It did not. Now he hopes that its Western backers, lacking the heart for a long struggle, will cut arms shipments and press Ukraine to sue for peace. They must not. Mr Putin is trying to show strength because he is weakened and the Russian people are beginning to sense it. Ukraine must maintain the momentum on the battlefield. Peace will come when Russian citizens understand that Mr Putin is losing and cannot win."
