SEASIDE, Calif.—Mike Gravel, a former U.S. senator from Alaska who read the Pentagon Papers into the Congressional Record, has died. He was 91. Gravel, who represented Alaska as a Democrat in the Senate from 1969 to 1981, died Saturday, according to his daughter, Lynne Mosier. Gravel had been living in Seaside, California, and was in failing health, said Theodore W. Johnson, a former aide. In 1971, Gravel led a one-man filibuster to protest the Vietnam-era draft and he read into the Congressional Record 4,100 pages of the 7,000-page leaked document known as the Pentagon Papers, the Defense Department’s history of the country’s early involvement in Vietnam. Gravel reentered national politics decades after his time in the Senate to twice run for president. Gravel, then 75, and his wife, Whitney, took public transportation in 2006 to announce he was running for president as a Democrat in the 2008 election ultimately won …