[William McKinley]

There was probably no response from the audience because they were sitting there in stunned silence.

[Catspaw]

I believe "stunned silence" is a fairly accurate description of the crowd's reaction:

The gathering, which included many Thurmond family members and past and present staffers, applauded Lott when he said "we're proud" of the 1948 vote. But when he said "we wouldn't have had all these problems over all these years" if Thurmond had won, there was an audible gasp and general silence.