Debate over slavery continued in Congress, and abolitionists proposed its end in the District of Columbia, where Congress had jurisdiction. Pierce supported a resolution by Calhoun against this proposal, which Pierce considered a dangerous stepping stone to nationwide emancipation.[42] Meanwhile, the Whigs were growing in congressional strength, which would leave Pierce's party with only a small majority by the end of the decade.[43]
One topic of particular importance to Pierce was the military. He challenged a bill which would expand the ranks of the Army's staff officers in Washington without any apparent benefit to line officers at posts in the rest of the country. He took an interest in military pensions, seeing abundant fraud within the system, and was named chairman of the Senate Committee on Military Pensions in the Twenty-sixth Congress (1839–1841). In that capacity, he urged the modernization and expansion of the Army, with a focus on militias and mobility rather than on coastal fortifications, which he considered outdated.[44]
Pierce campaigned vigorously throughout his home state for Van Buren's re-election in the 1840 presidential election. The incumbent carried New Hampshire but lost the election to the Whig candidate, military hero William Henry Harrison. 