Democratic presidential contenders are in a feverish battle to one-up each other with ever-more-ambitious plans to beat back global warming , curb gun violence , offer universal health care coverage , slash student debt and preserve abortion rights . Largely left out of the policy parade: immigration.

The field of 24 candidates is united in condemning President Donald Trump’s support for hard-line immigration tactics, particularly his push to wall off as much of the U.S. border with Mexico as possible, roll back asylum rights for refugees and since-suspended efforts to separate immigrant children from their parents. But only two contenders — ex-Obama Housing Secretary Julián Castro and former Rep. Beto O’Rourke — have released detailed, written policies addressing the future of the immigration system.

The dearth of formal policy plans signals the challenge that immigration could pose for Democrats. White House hopefuls can easily rally their party’s base with broad, passionate attacks on what they see as Trump’s failures, but it’s riskier to grapple with the complexity of the immigration system. Trump, meanwhile, has tapped into fervor around immigration to energize his own supporters and has worked to seize on it as an issue of strength — territory Democrats risk ceding to him ahead of 2020 if they don’t find a way to go deeper.

“For the most part, the Democrats aren’t even trying to make the case to a centrist voter of what a reasonable immigration plan would look like,” said Ali Noorani, executive director of the Washington-based National Immigration Forum, which works with faith leaders and law enforcement to promote the value of immigration. Undecided voters “know that Trump’s simplistic approach to this isn’t working,” Noorani said, “but they’ve got nowhere else to go.”

The issue isn’t likely to recede as the presidential campaign intensifies. Much of the Democratic field is heading this weekend to California — it borders Mexico and is home to the largest Hispanic population in the U.S. — for a state party convention. Meanwhile, the U.S. Border Patrol has said it plans to fly hundreds of immigrant families out of Texas as it struggles to process the large numbers of Central American families that are reaching the U.S. border with Mexico and asking for asylum.

Castro called in April for ending criminalization of illegal border crossings entirely. O’Rourke didn’t go that far in a plan he unveiled Wednesday , instead pledging to use an executive order to mandate that only people with criminal records be detained for crossing into the U.S. illegally. O’Rourke also promised to send thousands of immigration attorneys to the border to help immigrants with asylum cases while wiping out Trump polices separating immigrant families and banning travel to the U.S. from several mostly Muslim countries.

Other 2020 hopefuls have mostly focused on criticizing Trump rather than offering deeply articulated alternatives. Former Vice President Joe Biden, the early Democratic front-runner, has called Trump administration immigration policies an example of the president’s “demonization” of entire groups of people, but he hasn’t made the topic a top issue.

New York Sen. Kirsten Gillibrand has laid out a case for “comprehensive immigration reform” on her campaign website while Sens. Amy Klobuchar of Minnesota, Cory Booker of New Jersey and Kamala Harris of California have all previously voted for or sponsored plans to loosen immigration rules.

Then there’s Massachusetts Sen. Elizabeth Warren, who has issued a steady stream of sweeping plans on such issues as forgiving nearly all student debts and offering free tuition at public universities, but she hasn’t released a written immigration proposal. Spokesman Chris Hayden noted Wednesday that Warren has previously praised Castro’s plan and said the senator supports an immigration overhaul that creates a pathway to citizenship for immigrants in the country illegally, including those who came to the U.S. as children.

The Trump administration has proposed its own overhaul that would bolster border security while creating a “merit-based” immigration system prioritizing people with in-demand job skills rather than relatives of people already in the U.S. But that was largely seen as symbolic, and the president has repeatedly returned to his calls for extending the U.S.-Mexico border wall and imposing stricter immigration policies to excite supporters.

Feelings on the issue, meanwhile, are far from settled. About 54 percent of national voters said they disapproved of Trump’s handling of immigration policies, compared to 45 percent who approved, according to AP VoteCast, a survey of the 2018 national electorate.

Tyler Moran, who was a senior policy adviser to former Senate Democratic leader Harry Reid of Nevada, said that the primary campaign is still in an early phase and that candidates shouldn’t feel pressured to rush out policy positions on such a complicated issue.

“They have all said that they reject Trump’s approach and his vision of America and that we can do better,” Moran said. “Not everybody has packaged it together yet, but I think it’s coming, and I think every single one of them is prepared to answer the question of what they see as the plan on immigration.”

(AP)