Latino voters have the potential to swing the presidential election and several Senate races in November, but the group’s turnout remains a big question.

A new Pew Research Center poll found that fewer Latino registered voters are “absolutely certain” to vote this year, 69%, compared with 77% in 2012.

In contrast, 86% of all registered voters say they are absolutely certain to cast a ballot in 2016.

Several factors could contribute to the new numbers.

“This could potentially reflect less outreach from the campaigns than four years ago, or the growing presence of Millennials among Hispanic voters,” said Mark Hugo Lopez, Pew’s director of Hispanic research. Millennials in general have “traditionally had low voter-turnout rates,” he said.