In August 1846, Polk asked Congress to appropriate $2 million in hopes of using that money as a down payment for the purchase of Alta California in a treaty with Mexico. During the debate over the appropriations bill, Democratic Congressman David Wilmot of Pennsylvania offered an amendment known as the Wilmot Proviso, which would ban slavery in any newly-acquired lands. Though broadly supportive of the war, Wilmot and some other anti-slavery Northern Democrats had increasingly come to view Polk as unduly favorable to Southern interests, partly due to Polk's decision to compromise with Britain over the partition of Oregon. Unlike some Northern Whigs, Wilmot and other anti-slavery Democrats were largely unconcerned by the issue of racial equality, and instead opposed the expansion of slavery because they believed the institution was detrimental to the "laboring white man." The Wilmot Proviso passed the House with the support of both Northern Whigs and Northern Democrats, breaking the normal pattern of partisan division in congressional votes, but it was defeated in the Senate, where Southerners controlled a proportionally higher share of seats. Several Northern congressmen subsequently defeated an attempt by President Polk and Senator Lewis Cass to extend the Missouri Compromise line to the Pacific.