But turning Texas purple by 2020 would be difficult. Texas’s baseline partisanship is 11 percentage points more Republican than the nation — Trump won it by nine points while he lost the popular vote by two. So it would take an 11-point jump to make it a truly purple state that perfectly reflected the nation’s partisan divide.
That sort of a jump isn’t unprecedented: In 1988, New Hampshire voted for George H.W. Bush by 26 points in 1988, only to give Bill Clinton a one-point victory margin in 1992 and a 10-point margin in 1996. Iowa went from favoring Barack Obama by six points to favoring Trump by nine between 2012 and 2016. But most states don’t move that far in one cycle. Between 2000 and 2004, only two states — Alaska and Vermont — moved left as much as Texas would have to in order to become a truly purple state. Between 2004 and 2008, the baseline partisanship of Arkansas and Louisiana shifted wildly right and Indiana, while Hawaii (Barack Obama’s home state) shifted hugely leftward. But none of the other 46 states covered the distance facing Texas Democrats. In 2012, only one state shifted that far, and only five did in 2016.
The exact counts here will vary depending on methodology (feel free to email me with questions about my calculations), and reasonable people can set up different criteria for when a state is and isn’t purple. But the main point stands: An 11-point shift isn’t impossible, but it wouldn’t be normal.