What Changed? Late-Election Deciders (Jared McDonald Analysis of UMD/Nielson Research Poll)
While we can tell from party unity in the post-election survey that Republicans rallied behind Trump while the Democrats became less unified behind Clinton, the question remains as to whether Clinton supporters changed their minds to support Trump, or whether previously undecided voters broke heavily for Trump.
The results of the Critical Issues Poll suggest that late-deciders are largely the reason for the surge in support for Trump. In our pre-election poll, a full 15% of respondents claimed they had not made up their mind about who to support. In our post-election survey, we find that upwards of a quarter of the electorate made up their mind in the final month before the election. According to the results presented here, those who decided later were far more likely to support Trump.