During Blaine's six-year tenure as Speaker his popularity continued to grow, and Republicans dissatisfied with Grant mentioned Blaine as a potential presidential candidate prior to the 1872 Republican National Convention. Instead, Blaine worked steadfastly for Grant's re-election. Blaine's growing fame brought growing opposition from the Democrats, as well, and during the 1872 campaign he was accused of receiving bribes in the Crédit Mobilier scandal. Blaine denied any part in the scandal, which involved railroad companies bribing federal officials to turn a blind eye to fraudulent railroad contracts that overcharged the government by millions of dollars. No one was able to satisfactorily prove Blaine's involvement. Though not an absolute defense, it is true that the law that made the fraud possible had been written before he was elected to Congress. But other Republicans were exposed by the accusations, including Vice President Colfax, who was dropped from the 1872 presidential ticket in favor of Henry Wilson.