What a Russian assault on Ukraine would look like - YouTube by the Caspian Report
notes
U.S. Intelligence Sees Russian Plan for Possible Ukraine Invasion - The New York Times - Dec 4
with
Russia planning massive military offensive against Ukraine involving 175,000 troops, U.S. intelligence warns - The Washington Post
and I found
U.S. Intelligence Document on Russian Military Movements - The New York Times - Dec 3
Big mobilizations of troops and equipment east and northeast of Ukraine, enough for 175,000 troops, even if that number is not now present there. The WaPo article states that US assessments are at 70,000 troops, and Ukrainian ones at 94,000 troops.
The Caspian Report video has some discussion of a possible invasion plan. This plan has three waves of invasion, three waves in sequence with pauses for negotiations.
The first wave is in south Ukraine, starting from the Ukraine-Russia border and Crimea, going along the coast through Mariupol and Odessa. It will then go into Transnistria, a thin strip at Moldova's eastern border with a separatist movement.
The second wave has two subwaves. The first one starts in Donbass, at the east end of Ukraine, with Donetsk and Luhansk, where there is already a pro-Russian separatist movement. It goes west to the Dnieper River, which divides Ukraine into two roughly equal halves. The second one starts in the northeast, and goes through Kharkiv and Poltava before reaching the Dnieper.
The third wave also has two subwaves. One is from the north-northeast and heads toward Ukraine's capital Kyiv. The other one goes through Belarus and north Ukraine and also heads toward Kyiv. That city will thus be surrounded by Russian attackers.
What might happen if Russia does attack Ukraine? - YouTube by Binkov's Battlegrounds
Both the Caspian Reporter and Binkov discuss the relative troop and equipment strength on each side. Ukraine is rather behind Russia there, but it has the advantage of defense, and if they can hold out, that may make a lot of Russians discontented with the war.
The Caspian Reporter speculates that Russia won't want to dismember Ukraine, but instead give its provinces much greater autonomy, with not much for the central government in Kyiv to do.
In any case, that is likely to drive the unconquered parts of Ukraine much closer to NATO, and Sweden and Finland may end up joining that alliance.