You need nice runways and Russia will hit every single runway available
Flying them from Romania makes them useless as the combat range is significantly shortened, and using fuel tanks can give better ranges, but payload would be too low to be useful
Flying them for CAS would require basing close to Ukrainian front line, where Buk and Pantsir are going to be the main threats, even S300VM in Crimea and in Minsk or S400 which can see into Ukraine
Plus if you base them so close, iskander will visit it
All in all, it will be a threat, but not a game changer