U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

The screen of a video camera shows U.S. President Donald Trump speaking at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump speaks at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump (C) displays an executive order after addressing the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump (C) signs an executive order after addressing the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)

U.S. President Donald Trump (R) shakes hands with U.S. Attorney General William Barr at the International Association of Chiefs of Police Conference at the McCormick Place Convention Center in Chicago, the United States, on Oct. 28, 2019. (Photo by Joel Lerner/Xinhua)