In 1912 James decided to give up his House seat to seek election to the United States Senate.

He won that election in the Kentucky state legislature on 9 and 16 January 1912[3] and was sworn in on March 4, 1913.

His capabilities as a debater came to be recognized and feared in the Senate, as journalist and historian Claude G. Bowers observed:More than six feet tall and large in proportion, with an immense head and a smoothly shaven face that reflected every feeling, and with a powerful voice that could absorb all other sounds, he would have been a commanding figure in any legislative assembly.

In cold print his speeches lacked finish, but he relied on force, and his delivery accentuated the power of his argument.

In debate he rode the whirlwind to direct the storm, overwhelming his opponent with ridicule when unable to combat him with logic.