President Donald Trump’s immigration policies have been a failure. A mass of asylum-seekers has overwhelmed the system. Trump has sought to blame others, including the Democrats, who cry foul. But they too struggle for an effective answer.

From the day Trump announced for president, immigration has been his political go-to issue. It is the most-used weapon in his rhetorical arsenal and likely to be in the forefront in 2020. Whenever he needs to rally his supporters, whenever he needs a diversion from other problems, he has turned back to immigration.

His record speaks for itself. The man who calls himself a master dealmaker has never found a way to broker an agreement with Democrats to give him money for a border wall that, in 2016, he promised to build with money from Mexico. Having lost the most recent battle with House Democrats after a 35-day government shutdown, he declared a national emergency as a way to unlock funds elsewhere.

Last year, Trump and his Department of Homeland Security (DHS) were responsible for one of the biggest policy debacles of his presidency, the decision to separate children from their parents at the border. The ensuing backlash, which cut across party lines, eventually forced a reversal.

More recently, faced with a border that has been overwhelmed with asylum-seekers from Central America, he threatened to shut it all down. When businesses and his fellow Republicans protested that this would have damaging economic effects, he backed off.

This past week, he ran a buzz saw through the upper ranks of DHS, decimating the leadership there, including ousting Kirstjen Nielsen, the DHS secretary he had appointed. Now he talks of busing detainees into sanctuary cities in retribution for Democratic opposition to his policies.

For Trump, immigration is a proxy for many issues — national security, domestic security, cultural change, nationalism, even nostalgia. The president’s rhetoric inflames the left as much as it energizes loyalists, which is exactly his purpose. Democrats oppose Trump’s policies and resist when he seeks to blame them. They also point out that Trump tried to use immigration during the closing weeks of last year’s midterm elections, only to see his party lose its House majority.

Yet, for all the way he has manipulated the issue, immigration is also a policy conundrum, one that, whoever is president in 2021, will have to deal with. As a political matter, both sides seem willing to have the fight. Meanwhile, Democrats are also struggling to articulate policies to both solve the immediate problems at the border and insulate themselves from Trump’s charge that they are soft on illegal immigration.

One Democratic presidential candidate has taken up the challenge. Last week, Julián Castro, the former San Antonio mayor and former housing secretary, released a comprehensive immigration plan. During a CNN Town Hall, he said his approach represents “a completely different vision” than Trump’s, one built on compassion rather than criminality.

The Castro plan includes some policies long favored by Democrats and in the past by some Republicans. He advocates a path to citizenship for the millions of undocumented immigrants who already reside in the country and also for the Dreamers (the young people brought in as undocumented immigrants by their parents) and those with temporary protected status. That would require bipartisan support in Congress, which does not seem realistic at the moment.

Another proposal calls for a change in the law to make illegal entry into the U.S. a civil rather than a criminal penalty. In practical terms it would be a return to the de facto policy that existed a couple of decades ago, but it could also play into Trump’s hands, vulnerable to criticism that it would result in a more porous border.

Democrats have been more reactive than proactive. They have few answers for what to do about the current humanitarian problem, where a lack of resources — human and otherwise — has compounded it. Other than Castro, Democrats have been better at saying what they would not do than what they would — or saying nothing at all.