Putin tried this ‘on the cheap’ and doesn’t remotely have enough of a force mobilized to push through to Kyyv without Ukrainians being very soft and giving up.
Now he is in a tough place because he won’t want to give up and global support of Ukraine has emboldened Ukraine. Putin is already close to a stalemate without serious escalation via jet bombings. And it appears the Russian people themselves are not lockstep in this operation.
Had Russia only isolated his new republics, he might have gotten away with it, but he and his military appeared to completely misread Ukraine and even Russia on this.
In all fairness, it's only been a few days.
For Putin, the ideal scenario would have been to take over Kyiv in the first few days and cut the head of the enemy. But he can probably keep up the offensive for at least a couple of weeks before the pressure back home becomes intolerable. He can even win without occupying Kyiv, as long as he can get all the other cities he eventually wants to annex: Kharkiv (already fallen based on some reports), Mariupol, Odessa, etc.
But who knows the mind of a madman?
We're now already past the "peak outrage" from international community. In the coming weeks and months, Putin will wrap up his campaign, force Ukraine into some sort of submission either via ceasefire or by capturing the government and killing Zelensky, and crank up his propaganda machine and counter-sanctions to sow divisions within Europe and US. I have no high hopes for the resolve of the western nations in face of this crazy person.