Democrats accuse Republicans of suppressing the minority vote with laws to ensure ballot integrity. But then how do they explain record minority turnout last November? If Republicans were trying to stop minorities from voting, their schemes were inept.

The number of Latino voters nearly doubled in last year’s midterms compared to 2014 and came close to presidential year levels, according to a Pew Research Center analysis of new Census Bureau data. The share of blacks who voted climbed 10.8 percentage points to 51.4%, which...