Part of it is the same reason people have been predicting a blue Arizona for years: Latino voters. Along with the state’s small Black and Native American populations, Latinos constitute the Democratic base in Arizona. In 2016, a precinct-level regression analysis estimated that Clinton won more than 80 percent of the Latino vote in Arizona. And according to an analysis from the Center for American Progress, the share of eligible Latinos who voted also increased from 37 percent in 2012 to 42 percent in 2016.

And Arizona’s Latino population is swelling. The state has gone from 25 percent to 31 percent Latino since 2000. That said, the white population share in Arizona is still much higher (currently 55 percent). And many of Arizona’s Latinos are ineligible to vote: Among U.S. citizens who are 18 and older, white people are 65 percent of the population and Hispanic or Latino people only 23 percent. Worst of all for Democrats, low turnout rates mean Latinos constitute an even smaller share of the actual electorate: According to the CAP analysis, 2016 voters in Arizona were 73 percent white and only 17 percent Latino.

So this trend alone doesn’t explain Arizona’s sudden competitiveness, even though the Latino share of the electorate is slowly but surely increasing (it rose by 2 points from 2012 to 2016). The bigger factor at play is one that is not unique to Arizona, either: The movement of suburban voters from Republicans to Democrats since the 2016 election.