Updated 6:57 p.m. | Bowing to public pressure, President Donald Trump on Thursday signed an executive action ending the practice of separating migrant children from their parents amid a firestorm that saw congressional Republicans break with him.

The president contends Congress must pass legislation addressing the matter for it to be permanently solved given existing laws and court rulings his administration says mandates a process under which migrant children are separated from their parents when caught trying to illegally enter the United States. And it appears families can only be held together for 20 days, unless a federal judge alters a previous ruling placing a limit on detaining migrant families together.

Gene Hamilton, a senior counselor to Attorney General Jeff Sessions, said that judge has a “simple decision” to make in mulling a coming Trump administration request to adjust her ruling to keep the families together longer.

“Are we going to be able to detain alien families together, or are we not?” Hamilton told reporters Wednesday. “It’s clearly lawful, Congress has not passed any statute that prohibits the detention of families together. But the simple fact of the matter is, Judge Gee has put the executive branch into an untenable position.”

Other administration officials reportedly said families already separated will not be reunited.

“We want to keep families together,” Trump told reporters earlier Wednesday. “At the same time, we have to be strong on the border.”

The order represents yet another policy flip-flop by Trump. It also is a major loss for immigration hardliners like White House chief of staff John Kelly and senior domestic policy adviser Stephen Miller — and the president himself, who has been using tough immigration rhetoric since launching his 2016 campaign.

Trump Signs Order to End Family Separation Policy, Calls on Congress to Act

The president and White House have been under intense pressure, including from Republican members, to end the separation practice that stems from the administration’s policy to attempt to prosecute every adult nabbed trying to cross the U.S.-Mexico border illegally. The order reportedly would allow children and parents to be detained together while the adults awaiting a court hearing because it keeps in place the administration’s “zero tolerance” policy of trying to charge all adults with a misdemeanor.

“Going to be a lot of happy people,” Trump said from behind the Resolute Desk in the Oval Office a second before he put his large black felt pen to the order and wrote his signature. He said his daughter, Ivanka Trump, and first lady Melania Trump feel “strongly” about the matter and pressed him to act.

Even as Trump has answered lawmakers’ calls — Republicans and Democrats — his order could quickly be met by litigation from pro-migrant groups.

“This executive order would replace one crisis for another,” Anthony Romero, executive director of the American Civil Liberties Union, said in a statement issued before the president signed the order. “Children don’t belong in jail at all, even with their parents, under any set of circumstances. If the president thinks placing families in jail indefinitely is what people have been asking for, he is grossly mistaken.”

The White House has not yet clarified whether order is temporary or permanent. An initial review of its text shows no expiration date or congressional deadline, however.

Senate Minority Leader Charles E. Schumer on Wednesday morning said he the odds of both chambers being able to get a bill to the president’s desk are “just about zero.”

But, he said, “the percentage that the president could solve this problem if he wants to is just about 100 percent.”

A few hours later, Trump said this at the White House during an unrelated meeting with GOP lawmakers: “We’ve got to be keeping families together.”

Trump described the order as “somewhat preemptive, but ultimately matched by legislation, I’m sure.”

Watch: Democrats Flood House Floor With Children to Protest Family Separation

Some GOP members quickly expressed relief.

“I’m very pleased if this executive order brings a halt to this inhumane, traumatizing experience for these children,” said Sen. Susan Collins of Maine, adding said she still wants to see legislative action on the issue.

During the White House meeting, Trump “did say that there was still a need for legislation,” Senate Majority Whip John Cornyn of border-state Texas told reporters at the Capitol.

Earlier Wednesday, the president again blamed Democrats for the practice, but cryptically added this: “I am working on something.” Two White House officials were pressed on the matter, with both declining to describe a Fox News report about consideration of an executive order as inaccurate.

It’s the Democrats fault, they won’t give us the votes needed to pass good immigration legislation. They want open borders, which breeds horrible crime. Republicans want security. But I am working on something – it never ends!

— Donald J. Trump (@realDonaldTrump) June 20, 2018

White House officials also did not discount reports that the president would accept a stand-alone bill to end the separations. He had pressed members to include it in a broader immigration overhaul measure.

An executive order could halt the separations and be a swift policy reversal by the president and his team.

That’s because Trump said this early Tuesday afternoon: “Under current law, we have only two policy options to respond to this massive crisis: We can either release all illegal immigrant families and minors who show up at the border from Central America, or we can arrest the adults for the federal crime of illegal entry.”

[‘Trump Show’ Makes Tour Stop in Capitol Basement]

“So what I’m asking Congress to do is to give us a third option, which we have been requesting since last year — the legal authority to detain and promptly remove families together as a unit,” he said then.

Senior House Republicans even on Wednesday morning echoed the president and his top homeland security officials in saying a change to existing law would be required to end the crisis.

Members of both parties have rolled out or said they are working on legislation to fix what Trump and administration officials call “loopholes” they contend force them to separate families while parents are prosecuted. Senate Democrats have unanimously signed onto one bill, but no Republican senator has done so. Senate GOP leaders have signaled an intent to move a “straightforward” fix, maybe as soon as this week.

The Trump administration’s consideration of an executive action came less than 24 hours after the president huddled with House Republicans and expressed both moral and political concerns over the separation program he green-lighted in April. Since then, more than 2,000 children have been removed from their parents’ care while the adults await prosecution for the misdemeanor of trying to enter the United States illegally.

Watch: Why Are the Dreamers Called the Dreamers?

Earlier Tuesday — both on Twitter and during remarks at a small business conference in Washington — the president defended the policy.

Republican members emerged from their meeting with the president and said he prefaced his call for them to address the separation matter by describing a fix as “the right thing to do.”

Knowing the president is aware of public perception, members were not shocked that he also warned them the images of children wailing as their parents are taken away and of infants and toddlers in cages could lead voters to punish GOP candidates in November.

Speaker Paul D. Ryan opened a GOP leadership news conference Wednesday emphasizing that House Republicans do not support the separation of children from their parents. He said the House will vote Thursday on a measure that will fix the issue at the border.

“Families will remain together under DHS custody through the length of their proceedings,” Ryan said, noting the bill includes funding that DHS can use to provide housing for these families.

[House Immigration Compromise Faces Dim Prospects Amid Conservative Opposition]

During his meeting with House Republicans, Trump took no questions. Nor did he mention several House and Senate bills that have been rolled out or are in the works that would end the separation practice. But he instructed lawmakers to act after his administration has said its hands are “tied.”

The George W. Bush and Barack Obama administrations, subject to the same laws and rulings, opted against splitting kids from parents. Hardliners in the Trump administration chose to reverse that practice in April.

Republicans and Democrats have said in recent days that Trump has the authority to simply instruct federal law enforcement officials to stop separating migrant families.

“President Trump could stop this policy with a phone call,” GOP Sen. Lindsey Graham of South Carolina said during a Friday television interview. “If you don’t like families being separated, you can tell DHS, ‘Stop doing it.’”

Kellie Mejdrich contributed to this report.