Under fire from both Republicans and Democrats, Homeland Security Secretary Alejandro Mayorkas conceded Tuesday a surge in the number of children, mostly from Central America, is a challenge for the Border Patrol and other agencies amid the coronavirus pandemic.

But while rejecting a Trump-era policy of sending them immediately back to Mexico or other countries, Mayorkas acknowledged “we are on pace to encounter more individuals on the southwest border than we have in the last 20 years.”

“They are vulnerable children and we have ended the prior administration’s practice of expelling them,” Mayorkas said in his most detailed statement yet on a situation at the border that he characterized as “difficult” but not the crisis that critics have portrayed.

The U.S. government plans to house up to 3,000 immigrant teenagers at a convention center in downtown Dallas as it struggles to find space for a surge of migrant children at the border who have strained the immigration system just two months into the Biden administration.

American authorities encountered people crossing the border without legal status more than 100,000 times in February, a level higher than all but four months of Donald Trump’s presidency. The spike in traffic poses a challenge to President Joe Biden at a fraught moment with Congress, which is about to take up immigration legislation, and has required the help of the American Red Cross.

The Kay Bailey Hutchison Convention Center will be used for up to 90 days beginning as early as this week, according to a memo obtained by The Associated Press that was sent Monday to members of the Dallas City Council. Federal agencies will use the facility to house boys ages 15 to 17, according to the memo, which describes the soon-to-open site as a “decompression center.”

The Health and Human Services Department is rushing to open facilities across the country to house immigrant children who are otherwise being held by the Border Patrol, which is generally supposed to detain children for no more than three days. The Border Patrol is holding children longer because there is next to no space in the HHS system, similar to the last major increase in migration two years ago.

On Saturday, Mayorkas directed the Federal Emergency Management Agency to help manage and care for children crossing the border.

Asked about housing migrant teens at the convention center, White House press secretary Jen Psaki said Monday the administration has been looking for additional facilities for unaccompanied children but that she would have to look into the specifics of the arrangement in Dallas.

Biden has delighted pro-immigration advocates by backing a bill to offer a path to citizenship to all of the estimated 11 million people in the U.S. illegally. He also suspended several Trump-era policies to deter asylum, including one that forced them to wait in Mexico for court hearings in the U.S.

Republicans have seized on the numbers to portray a border spinning out of control. House Republican leader Kevin McCarthy and a dozen of his colleagues denounced Biden’s handling of increased migration at the southwest border and called for congressional action during a visit Monday to the Texas border.

The 13-person Republican congressional delegation traveled to El Paso following higher numbers of crossings at the U.S.-Mexico border, including thousands of migrant children arriving without their parents.

“This crisis is created by the presidential policies of this new administration,” McCarthy, R-Calif., said during a news conference.

Texas Gov. Greg Abbott issued a similar statement, blaming Biden’s policies for “a humanitarian crisis for unaccompanied minors coming across the border.”

U.S. authorities encountered children traveling alone 9,457 times in February, nearly double the number in January and the highest since May 2019, when the figure neared 12,000 during the peak of a Trump-era surge.

McCarthy blamed the recent influx on Biden’s efforts to undo his predecessor’s immigration restrictions. He also faulted Biden for not responding to a letter he sent earlier this month requesting a meeting to discuss recent migration trends.

“He doesn’t even acknowledge the letter, let alone a crisis that his policies created. So we will work together across the aisle, within our own party, because we know the solutions it will take,” McCarthy said.

If Biden does not reverse his immigration policies, “it’s going to take congressional action to do it, and that’s why we’re here,” he added.

Meanwhile, Democrat and GOP Senate leaders are casting doubts on Biden’s immigration plans. Comments from Sens. Dick Durbin, D-Ill. and Lindsey Graham, R-S.C., underscored that immigration remains a complex problem for the two parties to tackle successfully, even with Donald Trump no longer in the White House.

Republican demands to address the surge of young children and families at the Mexican border, plus a lack of needed support in both the House and Senate, were making passage of legislation unlikely, Durbin, his chamber’s No. 2 Democratic leader, told reporters.

“I don’t see a means of reaching that,” Durbin, a veteran of past efforts to strike an immigration deal, said of a comprehensive bill in this two-year Congress. “I want it. I think we are much more likely to deal with discrete elements” of such a plan.

Yet in the same conversation, Durbin said Graham’s insistence on addressing the stream of migrants at the border would make it hard to deal even with individual, broadly popular immigration proposals. Among those would be forging a pathway to citizenship for Dreamers — U.S. residents brought to the country illegally as children.

“When we start getting into the other areas, it gets much more complicated. He knows that,” Durbin said of Graham. The Democrat added later, “I wish we could move one piece at a time, but I don’t think that’s in the cards.”

Graham said the border problems make it “much harder” to reach an agreement. He told reporters that he believes a comprehensive bill won’t succeed this year.

“It’s going to be really hard to get a bipartisan bill put together on anything that has a legalization component until you stop the flow,” he said.

Biden has proposed creating a pathway to citizenship for the estimated 11 million immigrants in the U.S. illegally. He also wants to reduce long waits for some visas, enhance border technology and help Central American nations in hopes of diminishing the need for people to leave those countries.

Republicans in Congress have claimed that Biden’s support for immigration legislation and decision to allow people to make legal asylum claims has become a magnet for migrants, but Mayorkas noted that there have been surges in the past, even under Trump.