Upon his return to the United States in 1914, Haessler took a job teaching in the Philosophy Department of Illinois University at Urbana. He also continued work on his Ph.D., which he received upon completion of his dissertation, entitled "The Failure of Scottish Realism."
Politics
Haessler joined the Socialist Party of America in 1914. With American entry into the European conflict early in 1917, the ethnic German pacifist Haessler was dismissed from the university for his political views. He went to work for Victor L. Berger at his socialist daily newspaper, The Milwaukee Leader, remaining their for about a year. During this time he joined the News Writer's Union and the delegate of that organization to the Milwaukee Federated Trades Council. In the spring of 1918, Haessler was drafted into the U.S. Army. He accepted being drafted but refused to put on the uniform in boot camp and was therefore court martialed under military law. Haessler was found guilty and issued a sentence of 12 years of hard labor. Haessler completed just over two years of his prison sentence, served at the stockades of Fort Leavenworth and Alcatraz military prison from June 1918 until his being released in August 1920 by a presidential pardon. During Haessler's time in prison, his wife, Mildred Haessler, obtained a job as a teacher to support herself. During his time in prison, Haessler was removed for a brief period when he was called as a witness for the prosecution in the federal trial of Congressman Victor Berger. The prosecution attempted to demonstrate that Haessler's position as an imprisoned conscientious objector was a product of Berger's direct influence, thereby providing proof of Berger's criminality with respect to the current conscription law. Haessler would have none of it however, replying when asked if he and Berger had had any talks about the war:
Oh yes, I had lots of talks with Berger about the war. You see, I might say that I knew Victor Berger before I was born, since he knew my mother and father. But I don't remember what he said on those talks; I remember distinctly what I said, but his views did not impress me at all. I was far more interested in my views anyhow than I was in his.
Haessler characterized his views as significantly to the left of those of Berger, whom he called an "old fogey" that had told him "not to be a damned fool" and who had considered Haessler too young and rash and impulsive.
Federated Press
Upon his release, Haessler returned for a time to the employ of Berger's Milwaukee Leader before joining the fledgling Federated Press news service, a press agency which provided news copy to scores of radical and labor newspapers around the country. The Federated Press was initially established by E.J. Costello, former managing editor of The Milwaukee Leader. In 1922, Haessler was named as the managing editor and secretary-treasurer of the Federated Press, positions which he retained until the end of the news service in 1956. Haessler was also named associate editor of The Federated Press Bulletin, the weekly newspaper of the Federated Press issued for subscribers across America. In his capacities with the Federated Press, Haessler was a member of the International Typographical Union. In 1937, Haessler went to work for the Congress of Industrial Organizations handling the union's public relations from Flint, Michigan during its series of sitdown strikes there. He also served as editor of The United Auto Worker until 1941 and was a longtime editor of Tool and Die Maker's News.
Later years
Beginning in 1963, Haessler became involved in draft counseling of conscientious objectors to the Vietnam War.
Haessler married Lucy Haessler; they lived for many years at 39 Massachusetts Street in the Highland Park area of Detroit, Michigan. His sister, Gertrude Haessler, married William Weinstone, a high ranking-official of the Communist Party. Carl Haessler died age 84 on December 8, 1972.
