What can the west do about Russia invading Ukraine?

The 30-nation Nato alliance will stick to its pledge that it will never send forces to protect Ukraine as a non-Nato member. Backbench Tory calls to give Ukraine air support have no support in Nato.

The coordinated sanctions in Washington, London, Berlin and Brussels being announced on Thursday are billed as massive, but Putin sits on a $600bn (£450bn) war chest and will benefit from oil prices soaring past $100 a barrel. That makes him less dependent on the west to raise capital than five years ago, and such is his dominance of the Russian media that the chances of internal protests pressurising, let alone toppling, the 69-year-old president look minimal. The oligarchs may complain if sanctions are placed on them, but Putin is in too deep to retreat.

In the short term there will be a debate, including in Germany, about whether to arm the resistance, with some Green party and CDU leaders already advocating this.

There is also a danger that an insurgency would exacerbate a refugee crisis likely to be triggered across central Europe.

He may not invade the Baltic states, but he is in a better strategic position to demand a retreat by Nato to Warsaw pact boundaries and a land corridor through Poland to link Kaliningrad, the headquarters of the Russian Baltic fleet.

Finally, the west has to confront questions about the validity of the whole postwar diplomatic security architecture.