QUESTION: 1968 Convention Unrest

The liberals are making noises about blaming anarchists and radicals for any rowdiness that may happen at the RNC protests. Several liberal writers have argued that the riots at the 1968 DNC convention (initiated by the police of course) created a spectacle that caused Americans to support Nixon more. Was there any polling in 1968 that supports this contention, that the convention unrest swung Americans into supporting Nixon?