Just found another mass shooter data base. This one from Mother Jones and is from 1982.
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I counted the number incidences each year
1982 -1998: 0,1,2, or 3 incidences
1999: 5
2000-2006: 0,1, or 2
2007: 4
2008: 3
2009: 4
2010: 1
2011: 3
2012: 7
2013: 5
2014: 3
2015: 7
2016: 6
2017: 11
2018: 12
2019: 7 thru 8/4 (extrapolates to 12)
There can be little doubt that Trump has enflamed this epidemic.