Other events, however, have not had any detectable impact on voting intentions. We did not see any shifts after the release of the “Access Hollywood” recording, the second or third presidential debates, or the reopening of the FBI investigation into Clinton’s emails. When the same people were reinterviewed, almost all said they were supporting the same candidate they had told us they backed in prior interviews. The small number who did change their voting intentions shifted about evenly toward Clinton and Trump so the net real change was close to zero.
Although we didn’t find much vote switching, we did notice a different type of change: the willingness of Clinton and Trump supporters to participate in our polls varied by a significant amount depending upon what was happening at the time of the poll: When things are going badly for a candidate, their supporters tend to stop participating in polls. For example, after the release of the “Access Hollywood” recording, Trump supporters were 4 percent less likely than Clinton supporters to participate in our poll. The same phenomenon occurred last weekend for Clinton supporters after the announcement of the FBI investigation: Clinton supporters responded at a 3 percent lower rate than Trump supporters (who could finally take a survey about a subject they liked).