On this day, April 4 ...

1968: Martin Luther King Jr. is shot and killed while standing on a balcony of the Lorraine Motel in Memphis, Tenn.

Also on this day:

1841: President William Henry Harrison dies of pneumonia one month after his inauguration, becoming the first U.S. chief executive to die in office.

President William Henry Harrison dies of pneumonia one month after his inauguration, becoming the first U.S. chief executive to die in office. 1850: The city of Los Angeles is incorporated.

The city of Los Angeles is incorporated. 1917: The U.S. Senate votes 82-6 in favor of declaring war against Germany. (The House would follow suit two days later by a vote of 373-50.)

The U.S. Senate votes 82-6 in favor of declaring war against Germany. (The House would follow suit two days later by a vote of 373-50.) 1945: During World War II, U.S. forces liberate the Nazi concentration camp Ohrdruf in Germany. Hungary is liberated as Soviet forces clear out remaining German troops.

During World War II, U.S. forces liberate the Nazi concentration camp Ohrdruf in Germany. Hungary is liberated as Soviet forces clear out remaining German troops. 1949: Twelve nations, including the United States, sign the North Atlantic Treaty in Washington, D.C.

1975: Microsoft is founded by Bill Gates and Paul Allen in Albuquerque, N.M.

1976: The film “All the President’s Men,” starring Robert Redford and Dustin Hoffman as Washington Post reporters Bob Woodward and Carl Bernstein, respectively, has its world premiere in Washington, D.C.

1983: The space shuttle Challenger roars into orbit on its maiden voyage.

The space shuttle Challenger roars into orbit on its maiden voyage. 1988: The Arizona Senate convicts Gov. Evan Mecham of two charges of official misconduct, and removes him from office. (Mecham becomes the first U.S. governor to be impeached and removed from office in nearly six decades.)

The Arizona Senate convicts Gov. Evan Mecham of two charges of official misconduct, and removes him from office. (Mecham becomes the first U.S. governor to be impeached and removed from office in nearly six decades.) 1991: Sen. John Heinz, R-Pa., and six other people, including two children, are killed when a helicopter collided with Heinz’s plane over a schoolyard in Merion, Pa.

2008: Beyonce and Jay-Z are married during a private ceremony in New York.

2018: Saying the situation had reached “a point of crisis,” President Trump signs a proclamation directing the deployment of the National Guard to the U.S.-Mexico border to fight illegal immigration.