US Homeland Security Shake-Up Claims Political VictimsVOA News Center writer Ken Bredemeier contributed to this report from Washington. Department of Homeland Security Secretary Kirstjen Nielsen, who oversaw several contentious Trump administration immigration and border policies, will leave her post this week, opening up one of the most high-profile and influential positions in the president’s Cabinet. The move appears to be part of broader leadership changes at several agencies within the DHS, following a string of departures in recent days. On Monday, the White House said the head of the U.S. Secret Service (USSS) Randolph "Tex" Alles would step down. Three days earlier, President Donald Trump rescinded his own nomination for the director of U.S. Immigration and Customs Enforcement (ICE) Ronald Vitiello. The New York Times reported Monday that the head of the U.S. Citizenship and Immigration Services (USCIS), L. Francis Cissna, is also expected to step down soon, though neither the White House nor the agency has confirmed. According to Trump, the head of U.S. Customs and Border Protection (CBP), Kevin McAleenan — the country’s law enforcement agency at the border and at ports of entry — will temporarily take charge of DHS as acting secretary, which would mean a change in leadership at CBP as well. Heading in a 'tougher direction' The top-down shake-up is said to be motivated by Trump's interest in more restrictions regarding migration at the U.S.-Mexico border, and with immigration overall. In rescinding Vitiello's appointment last week, Trump said, “We want to go in a tougher direction" on immigration but did not elaborate. Nielsen’s departure comes after publicly conflicting with the president late last month over U.S. relations with Central America, and amid media reports that Nielsen did not go far enough in pushing Trump’s restrictionist agenda at the southern U.S. border. “Secretary Nielsen’s had a rocky tenure... from denying family separations were initially happening to having to justify the 'zero-tolerance' policy," said Krish O'Mara Vignarajah, president of Lutheran Immigration and Refugee Services. "This wasn’t altogether unexpected." With media reports that Trump wants to reinstate a policy of separating migrant children from their families at the border, the White House on Monday did not issue a flat-out denial of the allegation. WATCH: US immigration policy No media source currently available Hogan Gidley, White House deputy press secretary, told reporters: “The separation of families, you know, the president has said before he does not like that. It's a horrible practice. But Congress has a way to fix that so that it will not be a magnet for people to come here and use children to do it.” But migration is not triggered by one variable, such as congressional action, rather by several: conditions in migrants' home countries, policies in the United States, economic variables, weather. And that list changes. Neither Nielsen nor Trump, however, have publicly acknowledged that the administration's policies may in fact be contributing to the increased number of border-crossers in recent months, as Dree K. Collopy, chair of the National Asylum and Refugee Liaison Committee of the American Immigration Lawyers Association, suggested in January. Democrats welcome Nielsen resignation News accounts say Nielsen had no intention of quitting when she arrived at the White House on Sunday to meet with Trump, but that he was determined to ask for her resignation, which she submitted shortly after the meeting. White House sources have said Trump often yelled at Nielsen for apparently not being strong enough in curbing the number of migrants trying to enter the United States. "It is deeply alarming that the Trump administration official who put children in cages is reportedly resigning because she is not extreme enough for the White House’s liking," House Speaker Nancy Pelosi said in a statement following Nielsen’s announcement. Chairman of the Congressional Hispanic Caucus, U.S. Rep. Joaquin Castro, responded by summarizing Nielsen's tenure at DHS as "championing President Trump's cruel anti-immigrant agenda" and McAleenan's appointment "deeply disturbing" given the CBP commissioner's actions at the border. Castro went on to say McAleenan "cannot be trusted... based on his record of prioritizing Trump's harmful policies." But Nielsen's removal and McAleenan's temporary appointment are not a slam dunk on either side of the political spectrum. Noted immigration restrictionist Mark Krikorian, head of the Center for Immigration Studies, tweeted that he is "not sure McAleenan would be an improvement over Nielsen." He fully opposed Cissna's possible removal and said it would be a "colossal blunder." Trump has expressed frustration with the situation along the southern border, where hundreds of thousands of migrants trying to escape poverty and crime in Guatemala, El Salvador and Honduras have traveled through Mexico in hopes of entering the United States. Under U.S. law, foreign nationals are allowed to apply for asylum. Nielsen’s last day in office will be Wednesday, April 10. The Nielsen legacy Trump’s immigration policies created tumult at the border, in airports and in the court system. For the first year, former Homeland Security Secretary John Kelly carried out those decisions. His tenure largely focused on the first — and subsequent, controversial, and legally fraught — travel bans affecting international travelers and families with relatives abroad. The first successful attempt to cut refugee arrivals also happened under Kelly. Two of the three primary agencies tasked with refugee admissions are within the Department of Homeland Security. When Nielsen succeeded Kelly in December 2017, she led a shift toward more domestic-oriented policies, namely on the U.S.-Mexico border. McAleenan not only has led an agency that focuses on the domestic aspects of immigration, but who also has experience in law enforcement. O'Mara Vignarajah, head of LIRS, said that may reinforce Trump’s interest in clamping down on asylum-seekers. “We cannot effectively employ a law enforcement answer to what is a humanitarian problem," O'Mara Vignarajah said. "We just hope that Nielsen’s departure doesn’t allow for new leadership to be put in place doubling down on policies to turn away vulnerable women and children."