John Lewis to Clinton: 'Happy Birthday, Madame President'
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Rep. John Lewis (D-Ga.) wished former Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonThere are many unanswered questions about FBI culture FBI agent who sent anti-Trump texts offers to testify on Capitol Hill Giuliani wants 'full and complete' investigation into Russia probe's origins MORE a happy birthday on Thursday in a tweet calling her "Madame President."

Lewis's tweet Thursday afternoon had been retweeted more than 1,500 times less than a half-hour after it was posted.

Clinton won the popular vote for the presidency last November, but lost the White House to President TrumpDonald John TrumpEx-ethics chief calls on Trump to end 'monstrous' migrant policies Laura Bush blasts Trump migrant policy as 'cruel' and 'immoral' US denies report of coalition airstrike on Syria MORE in the Electoral College.

Lewis, a civil rights icon, endorsed Clinton and campaigned on her behalf. His tweet followed others from fellow prominent Democrats, including Clinton's husband, former President Bill ClintonWilliam (Bill) Jefferson ClintonBill Clinton hits Trump administration policy separating immigrant families in Father's Day tweet Trump's strategy for North Korea and beyond James Comey's higher disloyalty to America MORE.

Clinton, who turned 70 on Thursday, is currently touring the country as part of a national book tour for her memoir, "What Happened." The book examines the 2016 election and Clinton's eventual defeat to Donald Trump.