More than 29 million Hispanics will be eligible to vote in November's midterm elections, making up 12.8 percent of all eligible voters, both all-time highs that could prove critical as Democrats try to win control of one or both chambers of Congress, according to a report released Monday.

That overall increase is tempered by the fact that Hispanics have historically underperformed on Election Day compared with white and black voters, according to the analysis by the Pew Research Center.

The numbers are further undercut by the makeup of the increase: Of the 4 million additional Hispanics who became eligible to vote since the 2014 election, roughly 75 percent qualified by turning 18, meaning they’re part of the youngest voting bloc that also underperforms at the ballot box.

The net result is that Hispanics are likely to make up a larger share of all voters come Nov. 6 but not nearly as large as they could. Whatever the turnout ends up being could decide the outcome of dozens of races across the country, from tight Senate races in Hispanic-heavy states such as Arizona, Florida and Texas, to many House districts far from the border where Hispanics make up a larger share of the electorate.

As President Donald Trump fans the flames on immigration-related issues, the ability of the Republican and Democratic Parties to turn out Hispanic voters will be more important than ever.

"Every year, it's a mixed story," said Mark Hugo Lopez, director of global migration and demography research at Pew and co-author of the report. "There's the, 'Whoa, record number of Latinos turned out to vote,' but then their voter turnout rate declined. It's a hard concept to explain."

Hispanics have generally leaned Democratic, meaning that the rise in the Hispanic voter rolls should help Democratic candidates in their quest to retake Congress.

A clear example of that trend is in Florida, which features close statewide races for governor and U.S. senator. According to a separate report released by Pew on Friday, the number of Hispanics registering as Democrats in the Sunshine State since the 2016 election has increased by 5 percent, about double the rate for Hispanics registering as Republicans during that time.

The state has 837,000 Hispanics registered as Democrats, 527,000 registered as Republicans and 775,000 registered with no party affiliation, the fastest-growing group.

Monday's report from Pew shows that Hispanics make up a larger share of the electorate in more far-flung corners of the country. Though California, Texas, Florida and New York are home to more than 60 percent of the nation's Hispanic voters, states such as North Dakota and Oregon are seeing big Hispanic increases as well.

From 2014 to 2017, North Dakota had a 32.4 percent increase in the number of Hispanics eligible to vote, the largest percentage increase in the country, followed by South Carolina (30.1 percent), Oregon (28.8 percent) and North Carolina (28.2 percent).

All those increases will mean little if Hispanics don't show up Nov. 6. And if history is any indication, that will be difficult to achieve.

In the 2014 midterm election, Hispanic voter turnout was 27 percent, far below whites (45.8 percent) and blacks (40.6 percent) and barely edging out Asians (26.9 percent), according to the Pew study. The low Hispanic turnout is even more striking because that figure has been falling for decades, down from a high of 38 percent during the 1990 midterm to the 2014 figure, the lowest midterm turnout on record.

Lopez said several factors contribute to the decline in Hispanic voter turnout.

Since so many Hispanics live in states such as California and New York or congressional districts that are not competitive, they, like other voters, may not show up to vote, Lopez said. Hispanics skew younger than whites and blacks, leading to poor turnout among those who are 18-35. Lopez said polling makes clear that both political parties do a poor job connecting with Hispanic voters.

"Both Republicans and Democrats haven't necessarily reached Latino voters and asked them to vote," Lopez said.