President Donald Trump said he’s considering releasing migrants apprehended at the U.S. southern border into so-called sanctuary cities — largely Democratic municipalities that prevent their police from cooperating with federal immigration authorities.

Trump’s tweet followed a Washington Post report on Thursday that the administration had considered sending detained immigrants to sanctuary cities in retaliation against the president’s political adversaries. A spokesman for the Department of Homeland Security who asked not to be identified issued a statement minimizing the report late Thursday.

“This was a suggestion that was floated and rejected, which ended any further discussion,” the spokesman said.

Trump elaborated on the possible move later Friday during an event at the White House, saying predominantly Democratic cities and states, such as California, that have advocated for undocumented immigrants should take them.

“We’ll bring them to the sanctuary city areas and let that particular area take care of it,” Trump said. “We can give them an unlimited supply. Let’s see how happy they are.”

Trump has purged U.S. immigration leadership this week, including ousting Kirstjen Nielsen as secretary of Homeland Security, as he seeks to toughen his policies and stanch illegal crossings of the border with Mexico, a signature campaign pledge. But Senate Republicans are alarmed by the bloodletting within Homeland Security as well as the absence of any clear strategy to regain control of the border.

Meanwhile, a policy divide appeared to open among Republicans. Trump’s son-in-law and senior adviser Jared Kushner is developing an overhaul of the immigration system that is expected to increase legal immigration in an attempt to win bipartisan support. The White House is also weighing whether to implement a new regulation, called “binary choice,” that would give migrant parents detained after crossing the border the choice of surrendering their children to relatives, other caregivers or government-contracted shelters, or be detained together in ICE facilities indefinitely.

White House spokesman Hogan Gidley said the administration was calling on communities that had signaled a willingness to welcome undocumented immigrants in the past, suggesting the administration might pursue partnerships with state and local governments rather than targeting unwilling municipalities.

“Democrats say we must have open borders and that illegal immigrants have a right to be in this country at all costs, so they should be working with the administration to find the best ways to transport those illegal aliens that are already set for release, into communities in their states and districts,” Gidley said.

Trump has long criticized sanctuary cities and has periodically threatened to cut off federal funding for local governments that adopt policies protecting undocumented immigrants. It isn’t clear how a policy to release migrants into the cities would work, or how the government would ensure the immigrants stay there.

For one thing, the term “sanctuary city” itself is unofficial, created by opponents of immigrant-friendly policies to describe places that adopt them. There is no uniform definition of the policies that constitute a migrant “sanctuary,” nor any official count of how many cities have enacted such policies.

Under the government’s current practices, many apprehended migrants who claim asylum in the U.S. are issued court dates and are then released from temporary detention. Trump has derided the practice as “catch and release,” but the government doesn’t have enough space in detention centers to abandon it.

Even as hard-liners in the White House led by senior adviser Stephen Miller devise more aggressive immigration policies, the president himself has appeared wary of the political consequences. Trump has denied reports that he has recently debated reinstating last summer’s politically disastrous policy that led to separations of migrant children from their families, and has even disputed that a purge was underway at the Homeland Security department.

“I never said I was cleaning house,” Trump said on Tuesday.