In 1910, Victor Berger, a founding member of the Socialist Party of America, was elected to the United States House of Representatives representing Milwaukee, Wisconsin. The Russian Revolution had not occurred so being a Socialist was not a big deal. But being a Socialist and of German stock was a big deal when World War I started. Berger’s opposition to the war – and being a Socialist – landed him in court for violated the Espionage Act. He was convicted and sentenced to 20 years in jail in February of 1919 – AFTER the end of World War I. (The judge in that trial was Kenesaw Landis who later became the first Commissioner of Major League Baseball.) The Supreme Court overturned the conviction in January of 1921.
BUT, while on trial and during his appeal, Berger was re-elected to the United States House of Representatives in 1918. Congress refused to seat him in 1919 citing Section 3 of the 14th Amendment:
Section 3. No person shall be a Senator or Representative in Congress, or elector of President and Vice President, or hold any office, civil or military, under the United States, or under any State, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof. But Congress may, by a vote of two-thirds of each House, remove such disability.