"From the early days of the Trump administration, Stephen Miller, the president’s chief adviser on immigration, has repeatedly tried to use an obscure law designed to protect the nation from diseases overseas as a way to tighten the borders. The question was, which disease? Mr. Miller pushed for invoking the president’s broad public health powers in 2019, when an outbreak of mumps spread through immigration detention facilities in six states. He tried again that year when Border Patrol stations were hit with the flu. When vast caravans of migrants surged toward the border in 2018, Mr. Miller looked for evidence that they carried illnesses. He asked for updates on American communities that received migrants to see if new disease was spreading there. In 2018, dozens of migrants became seriously ill in federal custody, and two under the age of 10 died within three weeks of each other. While many viewed the incidents as resulting from negligence on the part of the border authorities, Mr. Miller instead argued that they supported his argument that President Trump should use his public health powers to justify sealing the borders. On some occasions, Mr. Miller and the president, who also embraced these ideas, were talked down by cabinet secretaries and lawyers who argued that the public health situation at the time did not provide sufficient legal basis for such a proclamation. That changed with the arrival of the coronavirus pandemic."