All those boos help Trump
George Bush is not popular with independents, not at all, and the Iraq War and the 2008 financial crash is not popular.
And Jeb rode a housing bubble and thinks he is a big genius. He makes Florida seem like a paradise, which is cause for a laugh by itself.
Trump will win S Carolina and it will be over.
Trashing GW was a way to minimize his value the same way he did Clinton. Not sure how highlighting the dynasty helps except with donors.