On May 16, 1868, the U.S. Senate failed by just one vote to convict President Andrew Johnson of “high crimes and misdemeanors,” as he was charged under the articles of impeachment. A second vote, taken on May 26, also fell short, by just one vote, of the two-thirds majority required to convict the president.
From the Library of Congress, which has details, though the contemporary report from The New York Times is more fun to read.