Lincoln's prohibition against emancipation, General Benjamin Butler at Fort Monroe Virginia declared slaves escaped into his lines as "contraband of war", that is, forfeit to their rebel owners. On May 24, Congress followed General Butler's lead, and passed the First Confiscation Act in August, freeing slaves used for rebellion. In Missouri, John C. Frémont, the 1856 Republican nominee for president, exceeded his authority as a General, declaring that all slaves held by rebels within his military district would be freed. Republican majorities in Congress responded on opening day of the December Session. Sen. Lyman Trumbull introduced a bill for confiscation of rebel property and emancipation for their slaves. "Acrimonious debate on confiscation proved a major preoccupation" of Congress. On March 13, 1862, Congress directed the armies of the United States to stop enforcing the Fugitive Slave Act. The next month, the Congress abolished slavery in the District of Columbia with compensation for loyal citizens. An additional Confiscation Act in July declared free all slaves held by citizens in rebellion, but it had no practical effect without addressing where the act would take effect, or how ownership was to be proved. Lincoln's preliminary Emancipation Proclamation was issued September 22, 1862. It became the principal issue before the public in the mid-term elections that year for the 38th Congress. But Republican majorities in both houses held (see 'Congress as a campaign machine' below), and the Republicans actually increased their majority in the Senate. On January 1, 1863, the war measure by executive proclamation directed the army and the navy to treat all escaped slaves as free when entering Union lines from territory still in rebellion. The measure would take effect when the escaped slave entered Union lines and loyalty of the previous owner was irrelevant. Congress passed enabling legislation to carry out the Proclamation including "Freedman's Bureau" legislation. The practical effect was a massive internal evacuation of Confederate slave labor, and augmenting Union Army teamsters, railroad crews and infantry for the duration of the Civil War. Joint Committee on the Conduct of the War Congress assumed watchdog responsibilities with this and other investigating committees. The principle conflict between the president and congress was found in the Joint Committee on the Conduct of the War. Eight thick volumes of testimony were filled with investigations of Union defeats and contractor scandals. They were highly charged with partisan opinions "vehemently expressed" by chair Benjamin Wade