U.S. President Donald Trump's top homeland security official joined officers as they carried out an immigration arrest in New York City on Tuesday, the latest effort to promote Trump's nationwide crackdown as enforcement has intensified in recent days.

In a display of force aimed at quickly increasing arrests and generating publicity, the administration targeted the nation’s largest city, where sanctuary policies limit official cooperation with ICE.

The administration has mobilized military units to head to the southern border and increased immigration raids in major cities. Here's what to know.