Halderman probably arrived in the Kansas Territory in October 1854. In November he became private secretary to the territory's first governor, Andrew Reeder. Subsequently, as secretary of the first territorial council in 1855, Leavenworth County's first probate judge in 1855-1856, a member of the territorial council of 1857, and a Douglas delegate to the 1860 national convention, he worked to make Kansas a Democratic state. But, like his Illinois mentor Douglas, in 1857-1858 he opposed the infamous Lecompton constitution, which sought to force slavery on an unwilling Kansas populace. He even purchased a partnership in the Leavenworth Journal as an oracle for that opposition. "While I controlled or owned it [the Journal]," wrote Halderman in 1881, "it favored a free state in Kansas, fought Lecompton, and supported Douglas." The split among "proslave" partisans over the ill-advised Lecompton effort further weakened the fledgling Kansas Democracy, and Halderman's party-building efforts were to no avail. The Free State (Republican) party won the day in Kansas, and at some point during the Civil War (probably in 1861), Halderman switched his party allegiance.
Virgil W. Dean, "Halderman, John Adams," American National Biography Online, February 2000, http://www.anb.org/articles/05/05-00307.html.