L. Francis Cissna, director of US Citizenship and Immigration Services, speaks at the White House in 2017.

According to the Washington Post, which first reported the resignation, former Virginia attorney general Ken Cuccinelli, a well-known firebrand who has, among other things, supported moves to restrict birthright citizenship, is set to replace Cissna.

“At the request of the President, I submitted my resignation today effective June 1, 2019,” Cissna wrote in the email. “During the past 20 months, every day, I have passionately worked to carry out USCIS’ mission to faithfully administer the nation’s lawful immigration system. We are the agency charged with safeguarding its integrity and promise.”

L. Francis Cissna, the director of the US Citizenship and Immigration Services, submitted his resignation Friday at the direction of President Trump, according to an email he sent to staff.

Cissna’s departure is the latest high-profile shake-up at the Department of Homeland Security (DHS) in recent weeks. It began in early April, when then-acting director of Immigration and Customs Enforcement (ICE) Ronald Vitiello had his nomination to lead the agency withdrawn by Trump. Soon after, then-DHS Secretary Kirstjen Nielsen stepped down, followed by the departure of the acting deputy secretary and chief of staff.

One source with knowledge of the White House’s thinking said Cissna was perceived as “lacking the leadership, assertiveness and executive savvy” to guide the administration’s biggest policy priorities in the second half of Trump’s first term.

“In terms of key administration priorities, the amount of unfinished work is extraordinary,” the source said. “Francis has been unwilling or unable to challenge the bureaucracy around him to strengthen asylum standards, close loopholes, advance pro-worker reforms, and take bold, decisive action to push policy and regulations through bureaucratic hurdles and roadblocks.”

Jessica Vaughan, policy director for the Center for Immigration Studies, a restrictive immigration group, also said it was “no surprise” some in the White House were impatient with Cissna’s steady and careful approach to making moves.

“Another difficulty for him was that his priority was reforming abuses in the legal immigration system and modernizing the system to benefit applicants, while some in the White House wanted the focus to be nearly exclusively on illegal immigration, and allowing businesses to avoid much scrutiny,” she said.

Cissna, who served for more than a decade at DHS, was appointed to lead the agency in the early days of the Trump administration. Since then, he has won the praise of immigration restrictionists who believe he dutifully carried out Trump’s campaign promises to stem the flow of immigrants, including pushing a proposal that immigrants who use or are likely to use public benefits, such as food stamps and housing vouchers, could be denied green cards or entry into the United States.

Elsewhere, Cissna cracked down on the H-1B visa system, announced plans to shut down international Citizenship and Immigration Services (USCIS) offices, and, in what many saw as a symbolic step, took out the phrase “nation of immigrants” from the agency’s mission statement. Under his direction, the agency was also considering moves to institute a fee for asylum applications and extend the time asylum-seekers needed to wait to obtain work permits.

“Francis Cissna knows the immigration system inside out, and that knowledge allowed him to spearhead some of the most restrictive legal immigration policies we’ve ever seen,” said Sarah Pierce, a policy analyst at the Migration Policy Institute. “The administration will likely be hard-pressed to replace him.”

Senate Majority Leader Mitch McConnell has previously signaled his displeasure with Cuccinelli, including telling reporters that he had told Trump not to take up the former Virginia attorney general as head of DHS.

“I’ve not spoken to him about any of them. I have expressed my, shall I say, lack of enthusiasm for one of them … Ken Cuccinelli,” he reportedly told reporters at the time.

Some Trump administration officials were dismayed with the move.

“The administration is making an aesthetic move that castrates the most effective immigration law practitioner in order to install a hero of the defeated right,” one official said.

One DHS official said Cissna had a “deep understanding” of the immigration system.

“He worked tirelessly to implement the President’s agenda and it’s hard to imagine someone else more qualified to do so,” the official said.