Trump stated on social media that his administration had transformed the nation's capital from "one of the most dangerous and crime-ridden cities in the U.S., even globally, into one of the safest places — in just a few weeks."
He accused Democratic Mayor Muriel Bowser of attempting to reverse this progress by ending the cooperation between the D.C. Police Department and U.S. Immigration and Customs Enforcement (ICE).
"Mayor Muriel Bowser, who has witnessed violent crime taking over our Capitol for years, has informed the Federal Government that the D.C. Police will no longer cooperate with ICE in deporting and relocating dangerous illegal immigrants," Trump said.
"If I allow this to happen, CRIME will return with a vengeance," Trump continued, before pledging to "declare a National Emergency and Federalize, if necessary!!!"
In mid-August, Trump issued an emergency declaration for D.C., deploying federal law enforcement and National Guard troops to address what he called "widespread crime" in the city.
However, the decree expired last week, requiring Trump to seek approval from Congress to maintain direct control over D.C.'s police force. The president currently has the backing of a majority of Republicans in both the House and Senate.
Mayor Bowser, a Democrat, has clashed with Trump on law enforcement and immigration issues. The District of Columbia has declared itself a "sanctuary city," limiting cooperation with federal immigration agencies.
Earlier this year, Trump sent National Guard troops to Los Angeles, California, amidst protests against his immigration policies.
Last week, the president announced plans to send troops to Memphis, Tennessee, and has previously mentioned the possibility of federal intervention in New Orleans, Baltimore, and Chicago.