“[T]he minority share of the electorate is growing,” and this favors the Democrats, assert Levitsky & Ziblatt. They then explain that the Republican response has been to limit participation by, inter alia, pushing for voter ID laws. These have “only a modest effect on turnout. But a modest effect can be decisive in close elections…” Pages 183-85.
First, increase in minority participation may be important to the national popular vote, but of course that is irrelevant to the question of who wins the presidency. The increase in minorities in the overall population arguably has motivated Republicans to vote for their nominee in swing states more than it has favored Democrats in swing states.
Second, the “modest effect” is especially critical in swing states. In a national popular vote system, voter ID laws would not matter much because their “modest effect” would be unlikely to alter the outcome.