sentences:  Dennison is credited with electing "Cowboy" James Dahlman mayor of Omaha eight times, and when losing an election, inciting the Omaha Race Riot of 1919 in retribution against the candidate who won.The son of Irish immigrants, Tom Dennison came to Nebraska from Iowa in 1860 at the age of two.When he was young, Dennison traveled throughout the West as a prospector, saloon-keeper, gambler and robber.