Elihu Root (February 15, 1845 – February 7, 1937) was an American lawyer and statesman who served as the Secretary of State under President Theodore Roosevelt and as Secretary of War under Roosevelt and President William McKinley. He moved frequently between high-level appointed government positions in Washington, D.C. and private-sector legal practice in New York City. For that reason, he is sometimes considered to be the prototype of the 20th century political "wise man," advising presidents on a range of foreign and domestic issues. He was elected by the state legislature as a U.S. Senator from New York and served one term, 1909–1915. Root was awarded the Nobel Peace Prize in 1912.
The first photographic image on pins dates to 1860. Abraham Lincoln and his various opponents used the tintype or ferrotype photo process. The first mass production of metal political buttons date back to the 1896 William McKinley campaign for president with "celluloid" buttons with one side of a metal disk covered with paper (printed with the message) and protected by a layer of clear plastic.
Since 1916, buttons have also been produced by lithographing the image directly onto the metal disk. A celluloid-type button is fastened to a garment using a pin on the back side of the button (in recently produced buttons, the pin generally fits into a safety-pin-style catch). A lithographed button may fasten with a pinback or with a metal tab which folds over a lapel or pocket.
One of the most famous uses of campaign buttons occurred during the 1940 U.S. presidential election, when Wendell Willkie's campaign produced millions of lithographed slogan buttons in rapid response to news items about President Franklin D. Roosevelt.
Time has a great feature on Campaign buttons, click here