FILE – In this April 3, 1968 file photo, the Rev. Martin Luther King Jr. stands with other civil rights leaders on the balcony of the Lorraine Motel in Memphis, Tenn., a day before he was assassinated at approximately the same place. (AP Photo, File)

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.
• 1850: 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.)
• 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.
• 1949: Twelve nations, including the United States, sign the North Atlantic Treaty in Washington, D.C.

Microsoft founder Bill Gates (Reuters)

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

Robert Redford and Dustin Hoffman as Woodward and Bernstein, the reporters who broke the Watergate scandal, in All the President’s Men. (AP File)

• 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.
• 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.)
• 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.

File -Jay Z and Beyonce. (Photo by Evan Agostini/Invision/AP, File)

• 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.

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• 2018:Facebook reveals that tens of millions more people might have been exposed in a privacy scandal involving Cambridge Analytica, a Trump-affiliated data-mining firm.
• 2018: After the United States says it would impose 25 percent tariffs on $50 billion of imports from China, Beijing quickly retaliates by listing $50 billion of products it could hit with its own 25 percent tariffs.