In 2018 Trump warned Germany not to become dependent upon Russian Gas

Obama did the same in 2014

https://www.reuters.com/article/us-usa-eu-summit-idUSBREA2P0...

And the Bush administration tried to prevent Nord Stream I.

https://www.spiegel.de/international/world/russia-s-energy-w...

Unfortunately there's some cold-hearted logic in buying cheap Russian gas for years, even if you know they will use the money to fund their incremental invasion of Ukraine.

As long as the one-off cost of switching to another supplier (or just reopening coal power stations, and re-certifying the nuclear power stations) is less than the accumulated annual cost of buying from more expensive suppliers in a pre-emptive boycott of Russia (who would just sell their gas to somewhere else instead) then ultimately Germany is saving money.

Importantly, (some of) the money that Germany was saving needed to be put into its own military preparedness and stockpiles, so that the foreign policy goal of protecting Ukraine's sovereignty could still be achieved (which would be a cost shared by other nations, including those further away from and thus less dependent on Russian gas).