During this period in Congress, Banks was one of the strongest early advocates of Manifest Destiny. He introduced legislation promoting offers to annex all of British North America (effectively today's Canada), which drew neither domestic interest, nor that of the Canadians. This and other proposals he made died in the Senate Foreign Relations Committee, chaired by Charles Sumner. They served to make him unpopular in Britain and Canada, but played well to his heavily Irish-American constituency. Banks also played a significant role in securing passage of the Alaska Purchase funding bill, enacted in 1868. Banks's financial records strongly suggest he received a large gratuity from the Russian minister after the Alaska legislation passed. Although questions were raised not long after the bill's passage, a House investigation of the matter effectively whitewashed the affair. Biographer Fred Harrington believes that Banks would have supported the legislation regardless of the payment he is alleged to have received. Banks also supported unsuccessful efforts to acquire some Caribbean islands, including the Danish West Indies and the Dominican Republic. He spoke out in support of Cuban independence.