  There is a widespread belief that the tone of US political language has
become more negative recently, in particular when Donald Trump entered
politics. At the same time, there is disagreement as to whether Trump changed
or merely continued previous trends. To date, data-driven evidence regarding
these questions is scarce, partly due to the difficulty of obtaining a
comprehensive, longitudinal record of politicians' utterances. Here we apply
psycholinguistic tools to a novel, comprehensive corpus of 24 million quotes
from online news attributed to 18,627 US politicians in order to analyze how
the tone of US politicians' language evolved between 2008 and 2020. We show
that, whereas the frequency of negative emotion words had decreased
continuously during Obama's tenure, it suddenly and lastingly increased with
the 2016 primary campaigns, by 1.6 pre-campaign standard deviations, or 8% of
the pre-campaign mean, in a pattern that emerges across parties. The effect
size drops by 40% when omitting Trump's quotes, and by 50% when averaging over
speakers rather than quotes, implying that prominent speakers, and Trump in
particular, have disproportionately, though not exclusively, contributed to the
rise in negative language. This work provides the first large-scale data-driven
evidence of a drastic shift toward a more negative political tone following
Trump's campaign start as a catalyst, with important implications for the
debate about the state of US politics.
