As Democratic presidential candidates have put out fresh policy proposals this year on a host of issues including education, child care, housing, climate change, student loan debt, taxes and inequality, President Trump has put forward new ideas at much the same clip.

They just happen to be almost exclusively about one issue: immigration.

On Thursday, he ratcheted up the pressure again by threatening to slap tariffs as high as 25 percent on all goods imported from Mexico — a move that risks harming the economy and undermining a trade deal he had been championing as a potential legislative achievement under divided government.

The wave of border policies flowing from the White House offers a clear signal that Trump’s reelection bid is likely to focus on immigration more than any other topic — a cause that animates his base but also highlights his failure to contain the flow of Central American migrants coming to the United States in record numbers.

“He certainly believes that immigration is a key issue that got him elected and, looking at the 2020 election, he’s trying to show that he’s trying to do something,” said Theresa Brown, a former policy official at the Department of Homeland Security who works at the Bipartisan Policy Center. “He knows that the situation that people are seeing every day shows that he’s not been successful. He has not secured the border.”

For a president who won an electoral college victory in 2016 based on a hard-line immigration message and a promise to make the Mexican government fund construction of a border wall, Trump’s latest gambit is an attempt to cover for the lack of progress on a signature campaign pledge, Brown said.

At the same time, many Democratic presidential candidates have struggled with how to respond. Most have sharply criticized Trump’s immigration rhetoric and approach, including the administration’s policy last year of separating children from their parents and the humanitarian conditions surrounding the deaths in recent months of Central American children in U.S. custody.

Out of nearly two dozen major candidates, only three — former housing secretary Julián Castro, former Texas congressman Beto O’Rourke and Washington Gov. Jay Inslee — have released detailed plans for reforming the immigration system. Most have kept their focus on health care and other issues.

“A country comprised of immigrants, asylum seekers and refugees — that’s our story, and we lose that story at our peril,” O’Rourke said during a roundtable discussion in Dallas with immigration experts and advocates on Thursday. “It has allowed us to become the greatest country in the world today, and we will lose that place of pride if we lose our way and our ability to continue to be this land of immigrants.”

Central American migrants with children are crossing into the United States at an accelerating pace, with more than 75,000 members of family units entering from Mexico in May, acting DHS secretary Kevin McAleenan told reporters on Thursday.

Trump announced Thursday that he would place a 5 percent tariff starting June 10 on all goods coming into the United States from Mexico, a move that would affect millions of products, including cars, produce and equipment. Trump said the tariffs would increase by five percentage points each month until Mexico stopped migrants from entering the United States.

“Mexico cannot allow hundreds of thousands of people to pour over its land and into our country — violating the sovereign territory of the United States,” Trump said Thursday in a lengthy statement. “If Mexico does not take decisive measures, it will come at a significant price.”

But business leaders, free-market conservatives and some Republican lawmakers warned that Americans ultimately will pay the price.

“Tariffs are taxes, plainly and simply,” Adam Brandon, president of FreedomWorks, a conservative group, said in a statement that criticized Trump’s announcement as an act of “usurpation” against congressional authority.

The president’s allies say he is taking action to address an emergency that Congress has ignored. They blame Democrats and the Mexican government for not stepping up to solve the problem that has overwhelmed the government’s capacity.

“President Trump’s tariffs on Mexico are a necessary response to the undeniable crisis on our border,” Trump campaign spokeswoman Kayleigh McEnany said in a statement. “Mexico has the power to stop this, and President Trump’s tariffs are a necessary step to catalyze action. Americans understand the crisis we face and the necessity of putting America First in addressing this crisis.”

McEnany said Trump would also plan to campaign on “the hottest economy on record.”

But the president’s focus as he gears up for his 2020 bid — Trump announced Friday that he would launch his official campaign on June 18 in Orlando — has been squarely on immigration.

Asked Thursday about new legislation in Louisiana to restrict abortion, Trump quickly changed the subject to the border, previewing what he said would be his “biggest statement so far.”

“We are going to do something very dramatic on the border, because people are coming into our country,” Trump told reporters at the White House.

Critics say it is the president’s flair for the dramatic that has worsened the situation at the border, as frenetic policies and statements emanating from the White House have added to a sense of chaos. Since December, Trump has attempted numerous strategies aimed at the border — from forcing a government shutdown to declaring a national emergency to threatening to close the border altogether.

None of it made a dent in the growing flow of migrants; border crossings are expected to surpass the April record of 109,000 in May.

As Trump has tried out different policy approaches, he has made his tough-on-immigration stance a centerpiece of his campaign speech. He often tells supporters at rallies that “the wall is being built,” when, in fact, the government is primarily replacing existing fencing, and promises there will be 400 miles of steel slats constructed before voters head to the polls in 2020.

He rarely mentions that the number of migrants apprehended at the border has grown steadily each month under his watch, a sign that his efforts so far have failed.

“His gut response to these things is toughen up the border, send the military, build the wall,” said Brown. “But the things he’s attempted to do have not worked.”

“The month of May is on pace to be the highest month in crossings in over 12 years and will significantly surpass the record 109,000 in April,” McAleenan said Thursday.

Democrats seeking to challenge Trump next year have offered a variety of approaches to the crisis and are increasingly being pushed to explain their plans for immigration.

At an immigration forum on Friday in Pasadena, Calif., Castro, Inslee and Sens. Bernie Sanders (I-Vt.) and Kamala D. Harris (D-Calif.) all promised to quickly pursue a comprehensive immigration overhaul if elected. Castro, a former Obama administration Cabinet member and the field’s only Latino candidate, released his plan in early April and said that “the next president must start by reversing the cruel policies of the Trump administration — including the Muslim ban, wasteful spending on a pointless wall and cuts to the refugee program — and ending the vile rhetoric that has scapegoated and vilified immigrants.”

Castro also has called for ending criminal penalties for migrants who enter the country illegally, a position that most other candidates have yet to embrace.

O’Rourke, who is from the Texas border town of El Paso, released his plan Wednesday and promised that, if elected, he would immediately reverse several of Trump’s immigration-related executive orders and policies, including those that encourage detention and deportation and that limit the number of migrants who can claim asylum. O’Rourke said he would also halt wall construction along the southern border.

Pete Buttigieg, a 2020 Democratic hopeful and the mayor of South Bend, Ind., has criticized Trump for using immigration as a political “wedge” to divide the country. He has said he believes a comprehensive immigration overhaul should include “a pathway to citizenship, a level of protection for “dreamers,” a set of reforms to clear up the bureaucracy, and reasonable measures on border security” — though he has not released any policy details that delve deeper than that.

The latest candidate to weigh in was Inslee, who released a plan Friday that calls for many of the same points outlined by Castro and O’Rourke. It would also push Congress to limit the power of the president in ways that would have prevented Trump from making it difficult for refugees to resettle in the United States and slow the asylum process.

Jenna Johnson and Amy Wang contributed to this report.