Homeland Security Secretary Kirstjen Nielsen on Monday effectively became the public face of the Trump administration’s “zero tolerance” strategy that has separated more than 2,000 immigrant children from their families over six weeks, offering a forceful defense of the practice while erroneously insisting that it was not the result of a new policy.

Pressed into service amid a maelstrom of bipartisan criticism, Nielsen addressed reporters at the White House’s daily briefing in an attempt to quell the mounting outrage over images of children crying after being taken away from their parents by Border Patrol agents at the southern border.

Yet Nielsen’s response, which at times contradicted itself, offered evidence that the administration — and perhaps Nielsen herself — was still struggling to formulate a message to counter critics who have accused the Trump White House of creating a humanitarian disaster.

“This administration did not create a policy of separating families at the border,” Nielsen declared. Questioned about whether the administration was using the immigrant children to try to force Congress to approve President Trump’s immigration agenda, she replied: “The children are not being used as a pawn. We’re trying to protect the children, which is why I’m asking Congress to act.”

That claim contradicts repeated declarations by administration officials in recent days that Trump believes separating families at the border will give him political leverage to force Democrats to agree to hard-line immigration policies. The surge in separations is a direct outgrowth of a “zero tolerance” border policy announced by Attorney General Jeff Sessions in April.

Nielsen’s role as the lead defender of the administration’s ­immigration policies follows months of worsening tensions between her and Trump, who has repeatedly berated the Department of Homeland Security chief in front of other White House officials and blamed her for the surge in border crossings that began earlier this year.

The spike has threatened to undermine Trump on his signature campaign promise in the lead-up to the midterm elections, and it has alarmed the president and his aides as the House prepares to vote on a pair of immigration bills this week aimed at finding consensus on an issue that has divided the party.

Nielsen’s contentious 20-minute appearance in the briefing room came as several prominent Republicans, including former first lady Laura Bush, have publicly joined Democrats in denouncing the family separations as callous and cruel.

Rather than offer a sense that the administration was reconsidering, however, Nielsen went on offense — alternately blaming past administrations, Congress and the media while seeking to focus attention on issues other than family separation.

“The narratives you don’t see are the narratives of the crime, of the opioids, of the smugglers, of the people who are killed by gang members,” Nielsen said. “So we don’t have a balanced view of what’s happening. But . . . the border is being overrun by those who have no right to cross it.”

In a speech to a law enforcement conference in New Orleans earlier in the day, Nielsen said the administration “will not apologize for the job we do.”

Nielsen has struggled to establish herself as the head of a sprawling government agency and win Trump’s confidence after White House Chief of Staff John F. Kelly successfully lobbied the president to name her to the top DHS job in December.

Nielsen, a former George W. Bush aide on homeland security, served as Kelly’s deputy when he led DHS for the first six month’s of Trump’s tenure and then joined him as a deputy at the White House.

Her ascension at DHS coincided with a spike in illegal immigration after the numbers had plummeted in Trump’s first year amid his harsh rhetoric and push for stricter enforcement. The influx has been driven largely by Central American migrants — many of them unaccompanied minors or women traveling with children — fleeing gang violence and drug cartels, an escalating crisis that also vexed the Obama administration.

Trump’s failure to win congressional funding for his border wall, and the stalemate on Capitol Hill over proposals to grant legal status to younger undocumented immigrants known as “dreamers,” led the administration to ramp up a series of enforcement measures.

Administration officials said the separation of children from their parents is the result of DHS’s new attempt to refer 100 percent of illegal border crossers to the Justice Department for prosecution. Under U.S. laws, they said, children cannot be held in federal jails, meaning they are placed in detention camps and shelters operated by Health and Human Services.

Lawmakers and journalists have reported on the conditions, and on Monday an audiotape featuring children sobbing and crying out for their parents was released by ProPublica, an investigative news site, which said it was recorded at a U.S. Customs and Border Protection detention center.

At the White House briefing, Nielsen rebuffed a reporter’s contention that family separations had not happened before the Justice Department’s “zero tolerance” announcement.

“That’s actually not true,” she said. “The last administration, the Obama administration, the Bush administration all separated families. . . . Their rate was less than ours, but they absolutely did this. This is not new.”

Cecilia Muñoz, a longtime immigrant rights advocate who served as White House domestic policy adviser under President Barack Obama, said in an interview that Nielsen was attempting to deflect criticism over a new policy specifically intended to send a message of deterrence to Central American families and to use the children as leverage in the ongoing legislative debate.

“She’s attempting to use technicalities to suggest that what’s happening is not happening,” Muñoz said. “The problem is, everyone can see it’s happening. That’s what prompted this moment of national revulsion.”

Some of the most intense outrage at the measures has followed instances of parents being deported to Central America without their children or spending weeks unable to locate their sons and daughters. In other instances, pediatricians and child advocates have reported seeing toddlers crying inconsolably for their mothers at shelters where staff are prohibited from physically comforting them.

The administration has defended its practice of keeping the children in government care while it conducts extensive background checks on those seeking to take custody of the children, including their parents.

Nielsen said the government has detected increasing instances of fraud among migrants traveling with children who are not their own.

But she bristled when a reporter asked whether the administration’s goal all along was to stir up public outrage.

“I find that offensive,” Nielsen said, “because why would I ever create a policy that purposely does that?”