Again, with what? Whether or not US supplies Ukraine have no bearing on how they engineering a Kyiv regime. That regime ain't going anywhere unless someone physically remove them, unless you are saying US physically invade Ukraine, that's would be another issue.
But as we see in the last 3 years of war, even up and down Russia failed to deliver, there are two best chance that they fumbled, one is when they initiate their attack, that is when they are the strongest, and they failed miserably, and the other is during 2023 when Trump withheld the aid package and hang out the Ukrainian to dry, that they only albe to take Avdviika and around 1200-1500 sq km territories. And since then EU stepped up miltiary aid a lot, and Russian forces degraded a lot. And you think somehow a miracle happens and Ukrainian line would just crumble?
Let me tell you what I know as an infantry staff officer who did intelligence and planning for a living.
To take the entire east side of Dnieper River, Russia would have to deal with around 60 strong point.
For the Russian to roll over the entire Eastern Ukraine (East of the Dneiper) There are 6 different fronts Russia have to cover They are (from top to bottom) Sumy Front, Kharkiv Front, Northern Donbas Front, Southern Donbas Front, Dnipro Front, and Zaporizhzhia Front
The key cities in Sumy Front is circle in black
Those are the city Russia HAVE TO take, they can't bypass it as those city control either the MSR/ASR or High Ground, if you don't take those city you don't have freedom of movement.
Other city such as Mykolaivka, Brozna, Putyvl and Ichnia are optional objective, you can either take them or bypass them, but if you by-pass them, you can't encircle the key cities, which mean it's going to take longer to fight in there.
Of those, Sumy itself is a large city, 150 sq km, with a lot of build up area, if we are using the Russian force progress in Bakhmut, it will take at least 3 times as long to take Sumy, and Bakhmut fought for 9 months. Romny, Pryluky, Nizhyn are similar in size with Bakhmut it will take arund 6 to 9 months to go over them, and Mala Divytsia is a small settlement, maybe you can take it in 3 months. That 6 cities alone will cost Russian 4 to 5 years progress. And then you also have the other minor objective to consider.
This is Kharkiv Front
Kharkiv front is bigger but similar deal with Sumy, all the black circle are important objective, You MUST take them if you want freedom of movement in the area, city between main transit route are again, optional objective
Kharkiv city itself is the SECOND biggest city in Ukraine. Dealing with Kharkiv alone can span years as you need to first taken Vovchansk, Chuhiv Bohodukhiv in order for you to encircle Kharkiv, Kharkiv itself is 350km, that city alone is going to take year to fall. Russia tried to go near them back in May 2022, and have to roll back in August the same year, then you have other cross road town and Kupiansk, Just taking all the key objective here alone would see around 9 years or a decade of work. Not including the optional cities.
This is Northern Donbas Front
As with the previous Russian battle plan, the key is to take the trio of "guard dog" first, Siversk, Lyman and Yarova, Russian successful taken Lyman and Yarova in the initiate stage, and then got rolled back, Siversk was seiged, never taken, and any plane to move West would first need to take the 3 cities, and then you need to wait until the Southern front to go up so you can Encircle Kramatosk and Sloviansk, which both city is similar in size with Sumy, which again, it will take 2 to 3 years there alone to felt that city.
And then you have 2 ways into the Ukrainian heart land and connect to Dnipro Oblast. Either go West from Sloviansk and thru Barvinkove or go West from the South via Porovsk.
This alone, will take anywhere from 6 to 8 years (around 2 years to felt all 3 Siversk, Lyman and Yarova, then 2 years each with Sloviansk and Kramatosk., and then another year or 2 thru Barvinkove and optional objective
You then have Southern Donbas
Toresk and Charsiv Yar is current operation, Toretask is already 7 months old battle. And Charsiv Yar is almost a year old. Then you are talking about Kostiantvika and Pokrovsk, Kostiantvika is not yet at war, Pokrovsk offensive is 7 months old again. Let's assume they all felt by the end of this year, then you have both Druzhkivka and Konstiantvika to take, let's say it's the same timeframe as Toretsk, it take roughly a year, so in 4 years, you may see Southern Donbas being conquer by Russian.
Then we move on to untapped territories, with more or less intact defensive line
This is Dnipro
Each of these city in black circle can easily last 1 or 2 years, with the City of Dnipro going to last more than 3 as this is even bigger than Sumy (410 or 450 sq km), you can't control Eastern Ukraine until Dnipro fall
Then the South is not any better
Zaporizhzhia is as big as Sumy, that city alone is going to be multiple years affair, then you have Orkhiniv to the south Porvoskse to the west, and Pavlohrad to the north east, all 3 are similar in size with Bakhmut. This is going to take about a year each for it.
You are talking about 4 to 6 years just to go up to Zaporizhzhia alone depending on your progress and whether or not you ignore the optional objective. And then the main even last for maybe 2 to 3 years.
Ukraine won't defend a city to the last men, the entire war they only ever do it twice once in Severodonetsk and the other time in Mariupol you are talking about 50-70% recycle rate which mean the loss of menpower is going to be around 40% each battle, which mean they can attrit the Russian invader.
So that alone will take 2 decade to achieve, Trump will be long gone, probably under the ground by then, it's impossible to in term to just take the key city alone.