Claudette Colbert was originally cast to play Mary Matthews. A few days before production began, Producer and Director Frank Capra fired her from this movie because she refused to work into the evening. Capra then hired Katharine Hepburn on Spencer Tracy's suggestion.
At the time this movie was released, President Harry Truman had not made his political comeback and was considered a sure loser in the 1948 Presidential election by nearly everyone. This is why the Republican Presidential nomination is considered so valuable in the movie, and why Van Johnson's character is amused when a young woman tells him that she thinks Truman will be elected President in his own right in November.
Adolphe Menjou was an ultra-right-wing political conservative who had eagerly co-operated with the House Un-American Activities Committee, named names of people he considered to be Communists, and was a strong proponent of blacklisting those whose political beliefs he didn't share. Katharine Hepburn was decidedly more liberal and had been an outspoken critic of the blacklist. Menjou had made several comments accusing Hepburn of being a Communist sympathizer, and possibly a Communist, which angered Hepburn and her co-star and romantic partner Spencer Tracy. Producer and Director Frank Capra was so concerned about the tension that he closed the set to the press.
Producer and Director Frank Capra originally wanted Clark Gable to play Grant Mathews so that he and Claudette Colbert could be reunited after their enormous success in Sucedió una noche (1934), also directed by Capra.
In the unedited version of this movie, where Grant Matthews (Spencer Tracy) is standing outside the White House and telling the little bookish fellow about all of the great people of history whose spirits live in the White House, he also lists Mohammad (founder of Islam). In the version broadcast on Turner Classic Movies (TCM), Mohammad's name was edited out, probably done when this movie was re-issued and new title and credit titles were printed (including three misspelled names). Note: When TCM aired this movie in 2019, Mohammad was included.