The reason why Russia hasn't declared war and fully conscripted the masses is the following:
1) it's politically costly as no Russians want to send their kiddies to Ukraine with a WW1 rifle and hardly no training and die, and
2) it will make no difference. Russia will still lose the war.
Every Russian knows what is happening in Ukraine. The west has been intercepting the phone calls of Russia soldiers from day 1. Their morale is obliterated. They are losing their comrades every day.
Russia is asking for peace negotiations but there will be no negotiations until Crimea is liberated.
We are looking at a desperate Russia now on the brink of total collapse. The only way out is a complete withdrawal. That is Russia's only solution. If they pull all their forces into Crimea, they have a chance of saving Crimea and a chance to withdraw into Russia if things get ugly as Ukraine has not destroyed the bridge yet. But don't expect the bridge to survive much longer. The only reason it hasn't is for humanitarian reasons and allow Russian forces to use it and leave Ukraine forever.
Slava Ukraine.