A Russian invasion isn’t an option. If Putin wants to lose, he’ll do that. An invasion will unite Ukraine and Russian armed forces will be lost in the vastness of Ukraine. The Russian military still is large but it also still is a conscript army. Mother Russia won’t like it when her sons are killing and getting killed by Ukrainian civilians. Ukrainians are far too closely related for that. It could split Russia and the Russian military. The risks are far too great. Putin understands all that.
He could create an excuse situation in eastern Ukraine and send in ‘peacekeepers’. But that supposes two things. One is that the opposition like in the Georgia conflict is stupid enough to give Putin the opportunity the way Mikheil Saakashvili did. Two is that a military incursion could benefit Putin. Neither suppositions are in evidence right now.
It is fortunate that the elections are planned for may, it’ll limit the Kremlin’s options to throw spanners in the works. Once a new government is in place, any provocation from the Kremlin will have to be much smarter.
Putin probably needs to do something, the Kremlin’s culture is ‘Russian-macho’. This loss is a sign of weakness. But his options are very limited, he may be looking to create a situation somewhere else to take people’s mind off Ukraine.