FIRST ON FOX: Twenty House Republicans on Monday wrote to Homeland Security Secretary Alejandro Mayorkas, demanding detailed answers about the Biden administration’s handling of the crisis at the southern border – and threatening a resolution of inquiry if the request is ignored.

The Republicans, led by Rep. Chip Roy, R-Texas, point to the continued surge in migrant encounters at the border, with more than 188,000 in June and reported preliminary numbers that indicate around 210,000 in July. Meanwhile, there were more than 830 unaccompanied children encountered in a single day at the border last week.

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While the Biden administration has blamed root causes like poverty, violence and climate change in Central America for the continued crisis, and has unveiled strategies to tackle those causes, Republicans have repeatedly blamed the Biden’s administration’s policies for fueling the surge.

"These numbers are appalling and are a direct result of the Biden administration’s weak border policies and your lackluster performance as the Secretary of the Department of Homeland Security," the lawmakers wrote in the letter, obtained by Fox News.

"DHS’s mission is 'with honor and integrity, we will safeguard the American people, our homeland and our values.’ Frankly, you are not fulfilling that mission," they wrote.

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The lawmakers demand a slew of information, documents and correspondence from the department, including a breakdown of the number of migrants brought into Customs and Border Protection (CBP) custody, the number of Border Patrol agents reassigned to facilities, the number of migrants who have tested positive for COVID-19 and have been released, and the amount of federal funding being spent on caring for migrants coming across the border.

In a sign of growing Republican pressure on both the administration and Mayorkas in particular, the lawmakers give a deadline of Sept.6 and warn that they will move to force an answer under House rules if the department does not respond.

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"If no response is received, we intend to introduce a resolution of inquiry under clause 7 of House Rule XIII that will require your department to respond," the letter says. "The American people and migrants seeking to come here deserve better than the chaos of a wide-open border."

The letter comes after both Roy and Rep. Andy Biggs, R-Ariz., have called for the impeachment of Mayorkas over his handling of the crisis.

"Over the past several months, President Biden and Secretary Mayorkas have blatantly and consistently refused to do their constitutional duty to take care that the immigration laws be faithfully executed, as required by Article II, endangering countless American and foreign lives in the process," Roy told Fox News Tuesday.

Biggs announced on Friday that he intends to introduce articles of impeachment against Mayorkas.

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Meanwhile, the administration has recently renewed the Title 42 public health order that allows for the rapid expulsion of migrants at the border, although it is not applying it to unaccompanied children and some migrant families.

Last week it announced that it is flying migrants rejected under Title 42 deep into the Mexican interior, citing the COVID-19 pandemic and the greater transmissibility of the delta variant.