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Before the start of business, Just Security provides a curated summary of up-to-the-minute developments at home and abroad. Here’s today’s news.

KIRSTJEN NIELSEN RESIGNATION

Kirstjen Nielsen will resign as Secretary of Homeland Security, President Trump announced yesterday, in a development illustrating growing the growing unrest within the administration over rising levels of immigration just days after the president retracted his threat to shut the Southern border. While under Nielsen’s watch the administration experimented with a range of draconian policies to deter migrants, the number arrested at the border in recent months has increased to the highest levels in more than a decade, Tess Hesson and Eliana Johnson report at POLITICO.

Replacing Nielsen on an acting basis will be Commissioner of Custom and Border Protection Kevin McAleenan. “Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service … I am pleased to announce that Kevin McAleenan, the current U.S. Customs and Border Protection Commissioner, will become Acting Secretary for @DHSgov …. I have confidence that Kevin will do a great job!” the president announced in a series of messages sent on Twitter yesterday evening, reportedly posted soon after he met with Nielsen at the White House. Nick Miroff, Josh Dawsey and Maria Saccheti report at the Washington Post.

“Despite our progress in reforming homeland security for a new age … I have determined that it is the right time for me to step aside,” wrote Nielsen in a resignation letter published to Twitter, hinting at the political difficulties she faced while in the role. “I hope that the next Secretary will have the support of Congress and the courts in fixing the laws that have impeded our ability to fully secure America’s borders and have contributed to discord in our nation’s discourse,” she added, Arnie Seipel, Laura Smitherton and Brian Naylor report at NPR.

McAleenan became the acting commissioner of the agency in January 2017 and was formally sworn in as commissioner in March 2018, managing a budget of over $13million. His priorities have included counterterrorism, border security and trade enforcement, Jacey Fortin reports at the New York Times.

“While Trump appears to have regarded Ms Nielsen as too feeble for the job … what she could have done to satisfy Mr Trump is unclear,” the Economist writes in an analysis of the developments.

Nielsen was hardly out of step with Trump’s stance on immigration, but her departure nonetheless marks a victory for conservative immigration voices such as White House policy adviser Stephen Miller, Stephen Collinson comments at CNN.

“Nielsen … whose legacy will be the most heartless and lawbreaking immigration policy this nation has known in at least 70 years … wasn’t heartless and lawbreaky enough for Donald Trump,” Michael Tomasky comments at The Daily Beast, arguing that “if there’s any justice in this world, she will spend her coming days thinking twice before traveling overseas for fear of being arrested for crimes against humanity.”

Nielsen has been sacrificed for Trump and his administration’s own failures at the border, the Wall Street Journal editorial board writes, arguing that Trump must move past his fixation on the long-promised border wall.

The TRUMP ADMINISTRATION: OTHER DEVELOPMENTS

White House acting chief of staff Mick Mulvaney has claimed that Congressional calls for six years of President Trump’s tax records to be released are a “political stunt.” The House Ways and Means Committee Wednesday made the rtax tax returns request to the Internal Revenue Service (I.R.S.) – but when asked during an interview on Fox News whether Congress would ever get sight of the returns, Mulvaney answered: “no, never … nor should they,” the BBC reports.

The reported security breaches at the president’s private Mar-a-Lago Florida retreat are a matter of grave public concern, Samantha Vinograd writes at CNN.

TRUMP-RUSSIA

Congressional Democrats are growing increasingly impatient with attorney general William Barr, who along with aides and other law enforcement officials are reviewing special counsel Robert Mueller’s report on Russian electoral interference and alleged collusion with the Trump campaign, reportedly still deciding on redactions. Charlie Savage provides an update at the New York Times.

Trump’s personal lawyer Rudy Giuliani claims that he wants the full Mueller report to go to Congress — stating “believe me, there was nothing there.” Appearing on CBS’ “Face the Nation” yesterday, Giuliani argued the president has nothing to hide and has demonstrated “unprecedented” cooperation with Mueller’s investigation, Matthew Choi reports at POLITICO.

“There are at least three reasons to believe — or at least to hope — that the version of the report Barr gives Congress will not include many material redactions … and that those Barr does make will not significantly affect Congress’s and the public’s ability to fully understand and assess the results of Mueller’s investigation,” Founding Editor Marty Lederman writes in an in-depth analysis at Just Security.

LIBYA

Eastern Libyan forces today made a push towards the center of capital city Tripoli after their “easy” desert advance reached a tougher urban phase. The eastern Libyan National Army (L.N.A.) forces of Khalifa Haftar reported that 19 of their soldiers had died in recent days as they closed in on the internationally recognized government in the capital; the U.N. reported that 2,800 people had been displaced by clashes, Reuters reports.

The U.S. has temporarily withdrawn some of its forces from the country due to “security conditions on the ground,” head of U.S. Africa Command Marine Corps Gen. Thomas Waldhauser announced yesterday. A small contingent of U.S. troops has remained in Libya in recent years, assisting local forces combat Islamic State group and al Qaeda militants; “the security realities on the ground in Libya are growing increasingly complex and unpredictable,” Waldhauser announced, the AP reports.

ISRAEL-PALESTINE

Israeli Prime Minister Benjamin Netanyahu said Saturday that he would annex Israeli settlements in the occupied West Bank if he wins another term in office, in a further potential threat to volatile Israel-Palestine relations. The announcement amounts to a reversal of decades of Israel’s policy acknowledging that the lands it seized in the 1967 war would be part of a negotiated settlement with the Palestinians; until now, Netanyahu had resisted pressure from settlers to formally annex or apply Israeli civil law in the region, Felicia Schwartz and Dov Lieber report at the Wall Street Journal.

“If Netanyahu wants to declare Israeli sovereignty over the West Bank … then you know he has to face a real problem,” Palestinian Foreign Minister Riad Malki commented yesterday in a reference to the fate of the millions of Palestinians who live there. “We will stay there,” Malki said of the West Bank, adding “the international community has to deal with us,”  Siobhán O’Grady reports at the Washington Post.

An analysis on the likelihood of Netanyahu following up on his pledge is provided by Merisha Gadzo at Al Jazeera.

IRAN

The Trump administration is today expected to designate Iran’s Islamic Revolutionary Guard Corps as a foreign terrorist organization, in a politically divisive step to increase pressure on Tehran. The move would mark the first time that an element of a foreign state has been officially designated a terrorist entity by the U.S., Michael R. Gordon, Warren P. Strobel and Nancy A. Youssef report at the Wall Street Journal.

Iranian lawmakers yesterday cautioned the U.S. against the designation. In a statement, 255 lawmakers warned that “we will answer any action taken against this force with a reciprocal action …so the leaders of America, who themselves are the creators and supporters of terrorists in the (Middle East) region, will regret this inappropriate and idiotic action,” Michael Burke reports at the Hill.

OTHER DEVELOPMENTS

U.S.-led airstrikes continue. U.S. and coalition forces carried out 250 airstrikes against Islamic State targets in Syria between March 10 and March 23 [Central Command]

A large explosion at a warehouse in Yemen’s rebel-held capital Aden yesterday killed at least 13 people, including seven children, and wounded more than 100, local medical officials said. The Iran-aligned Houthi rebels claimed the Saudi-led coalition had targeted the warehouse with an airstrike, though the coalition denied carrying out any strikes in the area, Ahmed Al-Haj reports at the AP.

Security forces in Sudan have responded forcefully to break up a protest by tens of thousands of peaceful anti-government demonstrators who have been camped for more than 48 hours in central Khartoum. Security forces have reportedly used teargas and baton charges on the demonstrators, Jason Burke reports at the Guardian,

Facebook took down a batch of more than 70 groups dedicated to cybercrime after they were flagged by researchers, according to a report published Friday.  Emily Birnbaum reports at the Hill.

A roundup of five “Very Important Things About the World Nobody Knows” is provided by Stephen M. Walt at Foreign Policy.