Last week we explored the shift in straight-party voting advantage in Republican-held districts toward the Democrats. Today we explore each party’s roles in those shifts.

Between 2012 and 2016, Democrats either cut into the Republican straight-party advantage or seized the advantage in 66 Republican-held legislative and congressional districts, 63 of which are on the ballot this year. Rep. Matt Rinaldi’s (R-Irving) HD115 and Rep. Rick Miller’s (R-Sugar Land) HD26 experienced the greatest “blue shifts” when measured as a percent of all votes cast in their district in 2016. In Rinaldi’s district, the straight-party advantage favored Republicans in 2012 by 5,471 votes. Four years later, the Democrats had an 1,835-vote advantage, a shift of 7,306 votes, equivalent to 12.4% of all votes cast in HD115 in 2016. Put another way, the shift in straight-party advantage is equivalent to one of out every eight voters going from casting a straight-party Republican (SPR) vote in 2012 to a straight-party Democratic (SPD) vote in 2016.

So, what actually happened in HD115? In 2016, 5,069 more people voted SPD than in 2012 and 2,237 fewer people voted SPR than four years earlier. Nearly a third of the “blue shift” in HD115 was caused by a decline in SPR voting.

Republican declines contributed to the “blue shifts” of 27 Republican-held districts, ranging from 2% of the shift all the way to 70%.

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