A US imposed no fly zone over Ukraine would pretty much end Russia.
Ehrm... what did you say??
A US imposed no fly zone, allowed Serbia to continue fighting for nearly a year - and that conflict still necessitated a political settlement at the end.
A US and NATO imposed no fly zone over Libya, failed to prevent any of the outcomes it was assembled against. Currently, Libya is divided between two halves - one ISIS controlled, and one Russia/Emirati controlled.
Never, in the history of the world, has a no fly zone succeeded in enforcing anything or producing facts on the ground. The only thing that matters - is infantry.
America enjoyed 20+ years of air superiority in Afghanistan - this did not prevent the collapse of the government they had been propping up for twenty years, in the space of two weeks.
Neither did America's dominance over the skies of Iraq, prevent the disasters that unfolded in Fallujah and Mosul.
Neither will America's current posturing off the cost of Venezuela, if it ever turns into an air campaign, force the collapse of Maduro's government.
Air power is nothing, without the ability to follow up on the ground, where you can secure and cement your gains.