Democratic U.S. presidential hopeful Hillary Clinton greets supporters at a "Latinos for Hillary" grass-roots event  in San Antonio. (Erich Schlegel/Getty Images)

The number of eligible Hispanic voters in the United States has expanded by more than 4 million since 2012, according to a new study, reaching a record 27.3 million ahead of the 2016 presidential election.

But whether they show up on Election Day 2016 is anyone’s guess; and if 2012 was any indication, they may not.

The growth among eligible Latino voters has been driven by the more than 3 million U.S.-born Hispanics who have matured into voting age since the last presidential election, according to the Pew Research Center study of the U.S. Hispanic electorate. But while the numbers are growing, there is a demographic reality that should give national Hispanic leaders and political strategists serious pause: The defining characteristic of the voting bloc is youth, with millennials now representing nearly half of all voting-eligible Hispanics in the United States.

Latino voters, in general, have a lower voter turnout than most other groups, and millennial voters are particularly unlikely to cast ballots.

In short, young Hispanic voters don’t vote. Or at least haven’t.

Hispanics represent about 12 percent of the total voting population in the United States, on par with the 12 percent share of voters who are African American, according to the study. Hispanic turnout in 2012, however, was just 48 percent — compared with 67 percent among black voters and 64 percent among white voters.

That number is even lower among Hispanic millennials, with just 38 percent showing up to the polls in the last presidential election. Black voter turnout among millennials, by contrast, was 55 percent; white voter turnout within the same age group was 48 percent.

There are enormous political undercurrents that will drive how Latinos vote this election, some based in tradition and others on the highly partisan political climate. Hispanics have gravitated toward the Democratic Party in recent years, but winning them over has remained an aspirational goal for Republican Party leaders. The rise of anti-immigrant rhetoric on the right from candidates such as Donald Trump could further alienate Hispanic voters — and potentially drive up turnout in support of Democratic candidates across the country.

Democratic presidential candidate Hillary Clinton has been particularly aggressive in courting the Hispanic community, appointing a high-profile political director who is the daughter of immigrants and making overtures to Latino community leaders across the country.

But whether the overtures or perceived insults coming from national political candidates will have an influence remains to be seen. Regardless, these voters could become the focus of voter turnout efforts in key 2016 battleground states such as Florida, Nevada and Colorado, where Hispanics make up between 14 percent and 18 percent of all eligible voters.

Read the full report from Pew Research here.