Early numbers suggest that voter turnout in 2016 wasn’t quite as high as many people expected. What’s more, weak turnout in key Democratic strongholds might have helped Donald Trump win a few crucial swing states.

The US Elections Project estimates that 131.7 million Americans cast a ballot in 2016, out of 231 million eligible voters — a turnout rate of 56.9 percent. This is still just a preliminary estimate, and states are still finalizing tallies, so check back for updates. But if those numbers hold, that’s a slightly lower turnout rate than 2012.

Lackluster turnout might have even cost Hillary Clinton key states. Voters in some Democratic strongholds who came out for Barack Obama in 2012 seem to have passed on Clinton this time around. And, as Domenico Montanaro of NPR points out, that could have been a difference-maker in Wisconsin and Michigan:

Clinton underperformed Obama in key counties with heavy black population. Was whole margin in Wisconsin and Michigan pic.twitter.com/hpC8ZcaLe9 — Domenico Montanaro (@DomenicoNPR) November 9, 2016

In case that tweet is hard to read, Clinton garnered 129,000 fewer votes in heavily Democratic Detroit than Obama did four years ago — and lost the state by around 61,000 total votes.

She also got 95,000 fewer votes in heavily Democratic Milwaukee than Obama did — and lost the state by 73,000 total votes. (Note that Wisconsin’s strict new voter ID laws may have prevented hundreds of thousands of people from voting this year.)

This obviously isn’t the only reason Trump won, but it’s an important subplot.

CNN has a more detailed breakdown of Clinton’s inability to turn out the Obama coalition: exit polls suggest she underperformed among African-American, Latino, and young voters (though given this year’s polling failure, we should take exit polls with a grain of salt). Before the election, a lot of people were mocking Donald Trump’s threadbare get-out-the-vote operation. But Clinton’s turnout problems may deserve scrutiny here.

Further reading

I took an in-depth look here at why 80 to 100 million Americans were likely to stay home in this election. Obstacles to voting (like long lines or restrictive voter ID laws) in some states likely played a role, but if history is anything to go by, so did pure disinterest and apathy.

Watch: The bad map we see every election