President Trump’s immigration policies have been a failure. His goal of sealing the border has come to naught, and a mass of asylum seekers has overwhelmed the system. Trump has sought to blame others, including the Democrats, for the problem. Democrats cry foul, but they too struggle for an effective answer.

From the day Trump announced his plans to run for president, immigration has been his political go-to issue. It is the most-used weapon in the president’s rhetorical arsenal and will likely be in the forefront of the 2020 campaign. 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 funding from Mexico. Having lost the most recent appropriations 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. The government is still trying to sort out what it wrought.

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 the ouster of Kirstjen Nielsen, the DHS secretary he had appointed. Now he talks of busing detainees to sanctuary cities in retribution for Democratic opposition to his policies.

For the president, 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 his loyalists, which is exactly his purpose. Democrats oppose Trump’s policies and cry foul 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 majority in the House.

Yet, for all the ways he has manipulated the issue, immigration is also a policy conundrum, one that whoever is president in 2021 will face. As a political matter, both sides seem willing to have the fight. Meanwhile, Democrats are also struggling to articulate policies that would 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 mayor of San Antonio and secretary of housing and urban development in the Obama administration, released a comprehensive immigration plan. During a CNN town hall, he said his approach represents “a completely different vision” from the president’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.

Julián Castro, a 2020 Democratic presidential candidate, speaks during a rally Wednesday in San Antonio. (Eric Gay/AP)

Another proposal calls for a change in the law that would make illegal entry into the United States a civil rather than a criminal penalty, allowing for more lenient treatment than the current law prescribes. 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 and be vulnerable to criticism that it would result in a more porous border? (For a fuller analysis of Castro’s plan, see the Vox article by Dara Lind.)

Democrats in Congress and on the presidential campaign trail have been more reactive than proactive on immigration. They have few answers for what to do about the humanitarian problem at the border, where a lack of resources — human and otherwise — has compounded the effect of the surge of asylum seekers. Other than Castro, Democrats have been better at saying what they would not do than what they would — or saying nothing at all.

Immigration will continue to animate Trump’s core supporters and will likely be one of two pillars of his reelection campaign. The other is the economy, the issue he will look to as a bridge to other voters whose support he will need to win what looks to be an extremely competitive election. Here, too, the Democrats appear to be struggling to find their own voice on what should be a central part of a presidential campaign message.

The new Battleground Poll by the Tarrance Group and Lake Research Partners under the auspice of Georgetown University’s Institute of Politics and Public Service shows the president holding a clear advantage over Democrats in Congress on which party people trust to deal with the jobs and with the economy. Democrats need to narrow or reverse that margin.

As an insurance policy, Trump has already gone on the attack against the Democrats on the economy, playing the “socialism” card. He has seized on Democratic proposals for a Medicare-for-all health-care plan and a Green New Deal, both of which in their most expansive iterations would require a heavy dose of government intervention and regulation, warning of dire consequences to the economy.

Candidates like Sen. Bernie Sanders (I-Vt.) and Sen. Elizabeth Warren (D-Mass.) have economic messages built around populist us vs. them themes, including attacks on big corporations and wealthy individuals. Their platforms contain the broad promise to rebalance the economic scales in favor of middle- and working-class Americans, in part through a variety of new taxes on those corporations and wealthy individuals. Warren in particular has offered a fresh list of detailed policies.

Most of the Democratic presidential candidates favor new taxes on the wealthy. But at this stage, most haven’t really said how they would pay for what they propose. The Democrats are often more focused on other issues than on the centrality of the economy in the lives of voters. Another sign of a lack of consensus in the party is the inability of House Democrats to agree on the outlines of a new budget.

The president has begun to set the themes for his reelection campaign. Democrats have vowed not to make the mistakes in 2016 of focusing too much on Trump’s fitness to be president. But they can’t ignore legitimate questions about how they would govern — or how they will credibly respond to the president’s attacks on his issues of choice.