What diplomatic effort? Imo, there is only push from EU and somewhat from US, while Russia has not done much but dead-on-arrival demands.
Yes, this is what leads me to believe that Putin has decided on an invasion in principle. Russia's diplomacy seems improvised, which is the opposite of what one would expect in a "bluff to gain concessions" scenario.
I agree. The Russian demands that NATO forces retreat to pre-1989 borders and "iron clad" commitments halting any future NATO expansion were clearly ludicrous and meant to be non-starters which the West wouldn't entertain much less accept. All Russian responses for calls for negotiation and diplomacy by the West have been along the lines of "there is nothing to discuss if our demands aren't addressed".
At this time none of the outcomes I imagine Putin wants (Donbass autonomy, a "neutral" Ukraine, etc.) can be accomplished without military intervention. Donbass autonomy was the most likely outcome not involving military action. Russia pursued the Minsk process, but Ukraine refused to accept any form of Donbass autonomy. Its leaders seeing it as accepting and institutionalizing Russian influence in the country. (I don't find that to be an unreasonable position, the breakaway regions were clearly not grassroots revolts organized by locals.) As time has passed, Ukraine has only gotten stronger militarily due to support, expertise, and training from NATO. This poses a threat to Russia's current sources of influence over Ukraine: the breakaway republics in the Donbass. A Ukranian takeover of the Donbass would end the key stategive Russian objective since 1991: having influence over post-Soviet states or as Russia calls it the "near abroad".
The tiny Baltic states joining NATO was frustrating to Russia, as it separated Kaliningrad (where much of the Baltic Fleet is stationed) from the motherland and brought NATO uncomfortably close to St. Petersburg. But it wasn't unacceptable to Russia. The same goes for a theoretical pro-Western EU or even reunified (with Romania) Moldova. A ding to Russian influence and prestige, but nothing major. But, a pro-Western NATO aligned Ukraine is completely unacceptable for Russia. A NATO Ukraine, even sans Crimea, severely limits Russian influence in the Black Sea (which was the whole reason why Crimea was annexed in the first place). The only way Russia will accept "losing" Ukraine would be through the specter international retaliation (and I don't mean just sanctions) or due to Russia's own weaknesses. That's exactly why since 2014, the Ukrainian government has been aggressively pursuing NATO membership. As long as Ukraine doesn't have a sufficiently subservient (or "neutral") government or the security guarantee of Article 5, Russia will continue to undermining it's authority and legitimacy. That includes the most extreme form of
undermining a government, military intervention.
