 Buchanan was appointed brigadier general of volunteers on November 29, 1862, but his appointment expired on March 4, 1863, having not been confirmed by the U.S. Senate.Historian Ezra Warner suggests that Buchanan's association with Fitz John Porter was the reason for the Senate's inaction on the nomination.Since the expired brigadier general appointment was Buchanan's only volunteer appointment, he reverted to his Regular Army grade of lieutenant colonel and brevet colonel and was not in the volunteer force.