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 ClintonIntel Dem decries White House 'gag order' after Bannon testimony 'Total free-for-all' as Bannon clashes with Intel members Mellman: On Political Authenticity (Part 2) 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 TrumpDems flip Wisconsin state Senate seat Sessions: 'We should be like Canada' in how we take in immigrants GOP rep: 'Sheet metal and garbage' everywhere in Haiti 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 ClintonTrump’s first year in office was the year of the woman Can a president be impeached for non-criminal conduct? Dems search for winning playbook 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.