The sleeping senator in the film, the one who when woke up says, "Opposed sir, diametrically opposed," was played by Henry Ashurst. Ashurst, who was no longer in politics when he appeared in the film, was Arizona's first senator after it was admitted to the Union.
shareOne of the first two, actually. Fellow Democrat Marcus A. Smith was the other.
Sadly, Henry Fountain Ashurst died just before this film had its debut, so never got the chance to see it.
Ashurst wasn't the only former senator in the film. Guy M. Gillette, an Iowa Democrat who served in the Senate from 1936-1945 and again from 1949-1955, has a couple of brief scenes, including one as one of the senators who passes the word to "wake up McCafferty" -- played by Henry Ashurst.