California Attorney General Xavier Becerra and the top cops in 18 other states and the District of Columbia urged President Donald Trump to uphold protections for young undocumented immigrants, also known as Dreamers, who came to the U.S. as children. They also vowed to help defend the policy against lawsuits from other states opposed to the program.

Former President Barack Obama’s administration implemented the Deferred Action for Childhood Arrivals program, also known as DACA, in 2012. The policy protects roughly 800,000 young immigrants from deportation, and allows them to work legally in the country, obtain driver’s licenses and apply to travel abroad.

On the campaign trail, Trump promised to “immediately terminate” the program, but has yet to do so. He’s since spoken sympathetically about Dreamers, describing some undocumented young people as “incredible kids” and claiming he’ll treat them with “heart.”

In their letter, sent Friday, the attorneys general referenced Trump’s more recent comments.

“Mr. President, now is the time to affirm the commitment you made, both to the

‘incredible kids’ who benefit from DACA and to their families and our communities, to handle this issue ‘with heart,‘” reads the letter. “You said Dreamers should ‘rest easy.’ We urge you to affirm America’s values and tradition as a nation of immigrants and make clear that you will not only continue DACA, but that you will defend it. The cost of not doing so would be too high for America, the economy, and for these young people.”

“For these reasons, we urge you to maintain and defend DACA, and we stand in support of the effort to defend DACA by all appropriate means,” the letter concludes.

In addition to California’s Becerra, the letter is signed the attorneys general of Connecticut, Delaware, Hawaii, Illinois, Iowa, Maine, Maryland, Massachusetts, Minnesota, New Mexico, New York, North Carolina, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, Washington and the District of Columbia.

Trump is also facing pressure from DACA’s opponents. Last month, 10 attorneys general and a governor threatened to sue the Trump administration if it doesn’t begin phasing out the policy by Sept. 5. On Thursday, the Justice Department declined to say whether the administration would defend the policy should those states sue. (U.S. Attorney General Jeff Sessions opposes DACA.)

Despite Trump’s softened rhetoric about Dreamers, the White House has indicated the president will not support bipartisan legislation to extend protections to them via legislation.