Facing widespread backlash to its "zero tolerance" policy that has resulted in the separation of migrant families at the southern U.S. border, the Trump administration have settled into a defensive posture, with the president blaming political opponents for his own directives.

After offering conflicting and false statements over the weekend about the policy and its consequences, President Trump and various officials defended their approach on Monday.

"Illegal entry is a crime. Illegal immigrants have put their children at risk," Department of Homeland Security Secretary Kirstjen Nielsen told reporters at the daily White House briefing. "DHS is no longer ignoring the law."

In a speech at the National Sheriffs’ Association meeting earlier in the day, Nielsen said the administration "will not apologize for the job we do, or for the job law enforcement does." The statement came just hours after she falsely claimed in a tweet that the administration did not have a policy of separating children from parents at the border.

“We cannot detain children with their parents, so we must either release parents and their children … or the adult and the minor will be separated as the result of prosecuting the adult," she said. "Those are the only two options.”

Attorney General Jeff Sessions, who announced the policy April, echoed those sentiments at the same gathering Monday. "We do not want to separate children from their parents," he said. "But we do have a policy of prosecuting adults who flout our laws to come here illegally instead of waiting their turn or claiming asylum at any port of entry. We cannot and will not encourage people to bring children by giving them blanket immunity from our laws."

At a White House event in the East Room, Trump argued that "the United States will not be a migrant camp, and it will not be a refugee holding facility." And even as his own party controls Congress, the president also issued a series of tweets attempting to pin blame on Democrats and arguing for broader immigration policy changes and concessions. "Children are being used by some of the worst criminals on earth as a means to enter our country," he tweeted. "It is the Democrats’ fault for being weak and ineffective with Boarder Security and Crime."

Meanwhile, troubling images of cages, foil blankets, and crying children at U.S. detention centers near the border seem to have cut across traditional partisan lines. All four living former first ladies have publicly opposed the program. "I appreciate the need to enforce and protect our international boundaries, but this zero-tolerance policy is cruel," wrote Laura Bush in an op-ed. "It is immoral. And it breaks my heart." And Melania Trump said she "hates to see children separated from their families."

Lawmakers in both parties traveled to border areas and detention centers over the weekend to survey the scene for themselves, and many expressed concern about the separation policy. Some have called on Trump to reconsider his approach. This comes as the president is slated to travel to Capitol Hill on Tuesday to meet with Republican lawmakers.

"The administration’s decision to separate families is a new, discretionary choice," Republican Sen. Ben Sasse of Nebraska wrote in a Facebook post urging Trump to reverse the policy. "Anyone saying that their hands are tied or that the only conceivable way to fix the problem of catch-and-release is to rip families apart is flat wrong."

New surveys show majorities of Americans disapprove of the administration's approach, though Republican respondents largely agree with it. A CNN poll found that 60 percent of Americans disapproved of the family separation approach, while 28 percent approved. Among Republicans, 58 percent approved, while majorities of independents and Democrats disapproved.

A Quinnipiac University survey found 66 percent of American voters in opposition while 27 percent were in support. Among Republicans, 55 percent approved, while 35 percent disapproved.

"When does public opinion become a demand that politicians just can't ignore? Two-thirds of American voters oppose the family separation policy at our borders," said Tim Malloy, assistant director of the Quinnipiac University Poll. "Neither quotes from the Bible nor get-tough talk can soften the images of crying children nor reverse the pain so many Americans feel."

House lawmakers are expected to consider two immigration-related bills this week. One measure, championed by a group of moderate GOP members, would offer legal protections for Dreamers -- young people brought to the country illegally by their parents -- and an eventual path to citizenship. Another measure, considered to be a more conservative proposal and sponsored by Judiciary Committee Chairman Bob Goodlatte, would provide temporary protections for Dreamers and would include cuts to legal immigration. Both would provide funding for a border wall -- and both have the president’s backing, Nielsen said during the White House press briefing.

Both measures are also expected to include language aimed at allowing children to remain with their parents while in detention, addressing a court order known as the Flores Settlement that bars the government from detaining migrant children. "The drafts of both bills clarify the Flores Settlement by ensuring accompanied alien minors apprehended at the border can remain with their parent or legal guardian while in DHS custody," a House GOP source said. "Drafters are also working to include a provision that not only addresses DHS custody but DOJ custody as well."

In addition to addressing that aspect of the current crisis, the administration is also asking Congress to reform asylum laws and to close what they see as legal loopholes. The administration has argued that its zero-tolerance policy was designed as a response to a previous "catch and release" program, in which illegal immigrants were seized at border and released into the United States to await a hearing. They argue that that policy created opportunities and incentives for those immigrants to come and stay in the country illegally.

In an interview with NPR last month, White House Chief of Staff John Kelly described the new policy, including the resulting family separation, as a "tough deterrent" for illegal immigration. "The big point is they elected to come illegally into the United States and this is a technique that no one hopes will be used extensively or for very long," he said at the time. Nielsen, however, called the notion of using family separation as a deliberate deterrent "offensive"

It's unclear whether immigration legislation could pass one or both chambers of Congress, given that lawmakers have been unable to pass previous measures to deal with former DACA recipients, and that midterm election politics complicate the ability to find agreement on contentious issues.

Some lawmakers have urged the administration to halt its policy until they can agree on a legislative fix.

"Separating children from their families at the border is a policy many of my constituents and the American people in both political parties oppose," Kansas GOP Rep. Kevin Yoder, who chairs the Homeland Security Subcommittee of Appropriations, wrote in a letter to Sessions. "As Congress pursues legislation to address this issue this week, an interim solution is needed. I ask that you take immediate action to end the practice of separating children from families at the border."

But the administration dismissed such calls. "We want to fix the entire system," White House spokeswoman Sarah Sanders told reporters.