> It seems like Putin went on tilt. It's hard to fathom any rational justification for this.
At least destabilizing Ukraine is necessary to prevent near-term, rapid decline for the Russian Federation. Ukraine's energy production potential and proximity to Europe make them a likely serious competitor, at a time when renewables are already putting pressure on petrostates like Russia.
Russia made Ukrainian resources in the East difficult to exploit with their fomenting or fabricating a persistent rebellion out that way, and seized most of Ukraine's substantial resources in the Black Sea when they took Crimea outright—but Crimea's dependent on Ukrainian fresh water, which has quite literally dried up for obvious reasons, and Russia's having a hell of a time (that is, spending huge amounts of money to limited effect) supporting Crimea without holding some of the mainland.
This is part of a series of actions aimed at creating short- and mid-term economic stability for Russia, while also improving their strategic situation. I would guess that an acceptable, if not perfect, outcome for them would be bringing the Eastern ~1/3 to 1/2 of Ukraine under Russian control, and it looks like they may yet manage to play their hand to effect such a partition, despite their bizarrely-inept invasion.
It does appear that they've blundered, overall, and not just though military fuck-ups—the sanctions are likely causing a ton of pain, NATO and the EU are more united against them than they've been in a long time and are re-arming (as in Germany), and they managed to bump energy independence way up the priority list for the EU. However, there are good reasons for them to (have tried to) do what they're doing.