President Trump said Mr. McAleenan, the commissioner of Customs and Border Protection, would “do a great job” taking over for Kirstjen Nielsen, who resigned Sunday.
President Trump has named a new “acting” cabinet secretary for Homeland Security, another in a series of temporary appointments that avoid a confirmation fight with Congress.
The president had blamed Ms. Nielsen for the rise in migrants who illegally entered the United States even though she supported his hard-line immigration policies.
Liberal Democrats are infuriated by a new Democratic Congressional Campaign Committee policy intended to protect centrist incumbents from primary challenges.
The House will formally file a lawsuit challenging President Trump’s declaration of a national emergency at the southwestern border, joining several others.
Joe Biden delayed his entry into the Democratic field, hoping to avoid the fray. Now, a crisis he was unprepared for has left him as badly bruised as anyone in the race.
A private lawyer retained by President Trump to fight Democratic demands for his tax returns told the Treasury Department that the request is an abuse of power.
The military tribunals originally barred public mention of what happened at C.I.A. prisons. Now a key question is what evidence terrorism suspects can use as the cases inch forward.