A new Syria is not likely to be pro israel/USA. it is no coincidence that I name these two countries in one breath. It could actually well be Iran being one of the driving forces for change in Syria. A Iran friendly governement would give them direct access to israels north east border and the first thing we may see is the taking back of the Golan Heights, Syrian land. So, i do not know why this 'aide' of Obama claims that Assad is bad for Israel, he has always maintained the peace and has not even claimed the Golan back, but there is no reason, looking at the other Arab Spring countries, to think that regime change would be beneficial for Israel and the USA.
Saudi-backed forces advance on rebel-held province in Yemen (DPA)
from the article: Obama aide: End of Assad regime will serve severe blow to Iran