There is a 19-year-old black man in Illinois who has no idea of the role he is playing in this election.
He is sure he is going to vote for Donald J. Trump.
And he has been held up as proof by conservatives including outlets like Breitbart News and The New York Post that Mr. Trump is excelling among black voters. He has even played a modest role in shifting entire polling aggregates, like the Real Clear Politics average, toward Mr. Trump.
How? Hes a panelist on the U.S.C. Dornsife/Los Angeles Times Daybreak poll, which has emerged as the biggest polling outlier of the presidential campaign. Despite falling behind by double digits in some national surveys, Mr. Trump has generally led in the U.S.C./LAT poll. He held the lead for a full month until Wednesday, when Mrs. Clinton took a nominal lead.
Our Trump-supporting friend in Illinois is a surprisingly big part of the reason. In some polls, hes weighted as much as 30 times more than the average respondent, and as much as 300 times more than the least-weighted respondent.
Alone, he has been enough to put Mr. Trump in double digits of support among black voters. He can improve Mr. Trumps margin by 1 point in the survey, even though he is one of around 3,000 panelists.
He is also the reason Mrs. Clinton took the lead in the U.S.C./LAT poll for the first time in a month on Wednesday. The poll includes only the last seven days of respondents, and he hasnt taken the poll since Oct. 4. Mrs. Clinton surged once he was out of the sample for the first time in several weeks.
How has he made such a difference? And why has the poll been such an outlier? Its because the U.S.C./LAT poll made a number of unusual decisions in designing and weighting its survey.
Its worth noting that this analysis is possible only because the poll is extremely and admirably transparent: It has published a data set and the documentation necessary to replicate the survey.
Not all of the polls choices were bound to help Mr. Trump. But some were, and it all combined with some very bad luck to produce one of the most persistent outliers in recent elections.
