Dem voters... the 19 point lead was only the week after the Dem Convention and reflected the inevitable dead cat bounce. Prior to the DNC, Dukakis held a 5 point lead over Bush.
After the GOP convention (1 month later) Bush held a 4 point lead.
https://www.latimes.com/archives/la-xpm-1988-08-24-mn-820-story.html