From a Department of Homeland Security shake-up to the arrest of Julian Assange, it’s been a busy week in American politics. Here are some of the biggest stories you might have missed (and some links if you’d like to read further).

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Trump’s Homeland Security purge.

Kirstjen Nielsen resigned as homeland security secretary on Sunday after meeting with President Trump, ending a tumultuous tenure that had made her a target of the president’s criticism. She is the latest in a long line of senior officials who have left the administration unceremoniously.

To placate Congress, Mr. Trump named a new “acting” secretary for homeland security. Such temporary appointments are seemingly becoming a permanent condition of the Trump administration.

A day after forcing Ms. Nielsen’s resignation, Mr. Trump accelerated a purge of the nation’s immigration and security leadership. At least five senior officials have been pushed out or are expected to leave in the coming weeks.