GDP is a measure of economic output. If your economy doesn't produce much then it is very hard to sustain a high intensity war.

But GDP is measured in dollars and not in amount of things produced. If everything is expensive in your country it will have larger GDP even producing less things.

Purchasing Power Parity calculations try to capture this.

Yes, but it is generally made around prices for cheap food and this doesn't help to understand how many cars, planes or rockets a country can produce.

Specially a modern war, in a foreign country were you can't play resistance. Modern war logistics are difficult and expensive.

Russia can turn into a war economy - which means GDP is nearly irrelevant. Right now they're doing warfare while still keeping the lights on at little inconvenience for the public. They can change that around.

You don’t just press a button that says “war economy” and then everything turns out fine. You drive massive inflation, weaken consumer markets, take on massive debts and eventually run out of young men.

Pretty much every nation bar the US was on the verge of economic collapse by the end of WWI (and Russia’s did). The financial burden of two world wars killed the French and British empires. Germany’s WWII war economy was totally unstainable and the USSR’s was bankrolled by the US lend-lease program.

It’s not a panacea - it’s just what you have to do to drive enough military production to sustain a near-peer conflict.

They can shift production from consumer goods to war goods, but total productive capacity won't grow dramatically. Productive capacity will likely decline due to the large number of able bodied men sent to their deaths or to be maimed.

The most valuable company in Europe is Louis Vitton. Forgive me, I don't think Putin's quaking in his boots about when they'll weigh in.

GDP was a good war metric for an industrial economy, and fucking terrible for a services based one. There's never one metric that describes all. You know it, Goodhart knew it, anyone was worked with metrics ever knows it. This is rather important and frankly I don't get the glibness. Russia's not an unstoppable force but it's not a joke either.