[1][2] Trimble subsequently joined the United States Army and served in the Mexican–American War with the 5th Indiana Volunteers, led by James Henry Lane.

[1][2] In the midst of his only term on the Iowa General Assembly, Trimble ran in the 1858–59 United States House of Representatives elections, losing to Samuel Ryan Curtis.

[2][3] Trimble left the state senate in 1860, and served in the Union Army as a lieutenant colonel of the 3rd Iowa Cavalry Regiment from 1861 to 1862.

[1] Trimble contested the 1872–73 United States House of Representatives elections for both the Liberal Republicans and the Democrats, losing to William Loughridge.

[3][4] Trimble later moved to Keokuk, where he continued to practice law, primarily representing the Chicago, Burlington and Quincy Railroad.