Latinos became the nation’s largest minority group in the early 2000s. Next year, the country’s pool of eligible voters is expected to include more Latinos than African Americans for the first time. But more than 10 years after black voters proved pivotal in nominating and electing the first African American major party presidential candidate, a Latino candidate has never come particularly close to winning the Democratic or Republican presidential primaries.

Julian Castro, of course, hopes to change that. So far though, he’s polling in the low single digits. Whether it’s Castro or another candidate in another election cycle, will Latino Democrats mobilize behind electing one of their own for president, as black Democrats have in the past?

Before we get to Castro, let’s start with understanding the role of the Latino vote in the Democratic primary process. While the eligible voter pool is expected to include more potential Latino voters then black voters in the 2020 general election, black voters are still likely to outnumber Latino ones in the Democratic primary. That’s true for several reasons, most notably because African Americans tend to vote at higher percentages and because Latinos are more divided between parties (about 25 percent are Republican and about 60 percent are Democrats) than African Americans are (close to 90 percent are Democrats). So part of the reason media coverage of the 2020 Democratic primary, including the coverage at FiveThirtyEight, tends to emphasize the role of black voters more than Latino voters is simply that there will likely be more black voters in the primary. As a rough estimate, I would expect somewhere from 18-25 percent of Democratic primary voters in 2020 to be black and 10-20 percent to be Latino.

But the size of the black vote is not the only reason it’s important in the primary — black Democrats also sometimes vote as a big, unified bloc. In four modern, competitive Democratic primaries, black voters overwhelmingly got behind one candidate — Jesse Jackson in 1984 and 1988, Barack Obama in 2008 and Hillary Clinton in 2016 — with more than 75 percent of the African American voters backing a single candidate, according to exit polls.

The Latino vote, in contrast, has tended to be less unified, regardless of whether a Latino candidate was on the ballot. The most prominent Latino Democrat to run for president was then-New Mexico Gov. Bill Richardson in 2008. He dropped out after lackluster finishes in Iowa and New Hampshire, so his campaign didn’t last long enough to compete in states with large Latino populations. The overall Latino vote is much smaller on the GOP side, but neither Sen. Ted Cruz of Texas nor Sen. Marco Rubio of Florida did particularly well in 2016 with Latino voters in any of the three states where we have detailed exit poll results — each won a plurality of the Latino vote in their home states, but President Trump won at least a quarter of Hispanic voters in both Florida and Texas and a plurality in Nevada.

The candidate who has done best with Latino voters in recent primaries is Hillary Clinton, but even her performance was not dominant. In 2008, Clinton won more than 60 percent of the Latino vote in the Democratic primary. In 2016, few exit polls were conducted in states with sizable Latino populations, but of the four states where we do have detailed results, Clinton basically split the Latino vote in Illinois and Nevada against Bernie Sanders, while winning about 70 percent in Florida and Texas.

What does all this history mean for Castro’s candidacy? Castro, who served as mayor of San Antonio from 2009 to 2014 and then as secretary of Housing and Urban Development in the Obama administration, is not a civil rights leader in the mold of Jackson or an already famous political figure like Clinton. But you could see him taking a path somewhat similar to another Harvard Law School graduate who ran for president in his 40s: Barack Obama.

In 2007, before the voting began, polls suggested that Clinton and Obama were running neck-and-neck among black voters. Then, Obama won Iowa and narrowly lost New Hampshire, two states with very small black populations. Once the primary moved to the South, Obama overwhelmingly won the black vote. It’s impossible to know for sure, but it seems likely that black voters moved decisively toward Obama as they saw that he had a real chance to win. And that black support helped Obama win many Southern states, including a number with heavily black Democratic electorates.

For Castro, then, the ideal scenario is that he is a viable candidate when the primaries start in February, so he can galvanize Latinos behind him in three key states in particular: California, Nevada and Texas. Nevada (where about 20 percent of Democratic primary voters are likely to be Latino) is currently scheduled to be the third state to vote. California and Texas, the two states with the largest Latino populations, hold their primaries along with several other states on Super Tuesday, on March 3, but both states allow early voting, so lots of voters in both states will cast ballots in February.

In short, Castro will have less time, post-Iowa, to show Latino voters he has a real chance. That means he’ll need to use Iowa and New Hampshire as a springboard as much as possible, while also trying to rally Latino voters for strong showings in Nevada, California and Texas regardless of what happens in the first two contests.

And it’s entirely possible that he will succeed in mobilizing Latino voters. Some research has shown Latino voters are more likely to vote if a Latino candidate is on the ballot and more likely to back the Latino candidate than a white one, even in an intra-party race. But that research largely looked at state- and city-level races — we haven’t had a major Latino presidential candidate on the Democratic side, where appeals to shared racial identity are easier to make than in the GOP.

“If Latinos think that Castro has a reasonable chance of winning, they will come out in large numbers to support him,” said Melissa Michelson, a political science professor at Menlo College and an expert on Latino political activism. She suggested having key Latino leaders embracing Castro’s candidacy would be important, with Michelson specifically naming journalist Jorge Ramos as a key potential validator for Castro.

Michelson’s caveat — “a reasonable chance of winning” — is important and goes back to the Obama comparison. Castro is currently polling at 1 percent in many surveys. He is raising significantly less money than some of his rivals, and it will take a lot of money to organize and win in big states like California and Texas. There are few polls that have large samples of Latino Democrats, but the fact that, in the few polls available, he’s not doing much better in California (where 30 percent of eligible voters are Latino) than in Iowa (where 3 percent of eligible voters are Latino) suggests that he is not overwhelmingly popular with that demographic.

For Castro to even test the potential for a Latino candidate to mobilize Latino voters in a Democratic primary, he needs to first do fairly well in contexts where Latino voters are not particularly powerful: fundraising, endorsements and debates.

Castro is an experienced politician, and he seems to know all of this. He is running a campaign not unlike Obama’s in 2008 or Cory Booker’s and Kamala Harris’s this year — some targeted appeals to his racial group but also a traditional campaign aimed at the broader Democratic base. I spent a day on the campaign trail with Castro last month in and around Charleston, South Carolina. Castro started the day visiting a black church, then went to the site where a black history museum is being built and later to a barber shop. In short, the former mayor was campaigning for the black vote, just as all the other presidential candidates do when they go to South Carolina, where African Americans are likely to be the party’s biggest voting bloc. He doesn’t want to be narrowly defined as the Latino candidate and realizes he can’t be defined that way if he wants to win.

At the same time, Castro, who is Mexican American, went to Puerto Rico in January for his first major trip after launching his campaign. His staffers are trying to organize the relatively small (6 percent) Latino population in Iowa and get them excited about Castro. He has called for a “Marshall Plan for Central America,” referring to the aid that the United States offered to help rebuild Europe after World War II. Castro is one of the few Democratic candidates to put out a comprehensive immigration proposal, with a group of proposals that would add up to a total reversal of the aggressive border security regime that has existed not only under Trump but also Obama and George W. Bush. He is not shying away from issues that disproportionately affect Latinos and could cast him as defending Latino interests.

When I asked Castro how he would present himself as “electable” to Democratic voters, he named six states that he felt he could flip: Michigan, Pennsylvania and Wisconsin, which Clinton barely lost in 2016, along with Arizona, Florida and Texas. Castro didn’t outright say this, but the implication was obvious: Arizona, Florida and Texas are the three states with the largest Latino electorates that did not vote for Democrats in 2016.

“It’s important to always campaign and to govern for everybody,” Castro said when I asked him about being the only Latino candidate in the race. “And I’ve always done that in public service.”

But, he added: “I recognize that there’s special meaning for the Latino community, especially now, because the community has been so targeted by this president, whether on the issue of immigration or his comments about the Mexican judge or any number of ways that he has scapegoated people. He has tried to paint people of color as the ‘other’ …. So I’m confident that my campaign is going to resonate with people of all different backgrounds, but of course there’s special meaning in the Latino community.”

Castro is doing exactly what he should be doing at this stage — trying to make himself a viable candidate to all Democrats while also laying the groundwork for Latino voters in particular to get behind him. But he probably has to be great at the first part to get a chance at the second part. And so far, the signs are not promising.

Presidential candidate Julian Castro on his 2020 campaign