Elected in 1908, Bristow served a single term in the United States Senate where he gained recognition for his support of several political causes of the Progressive Era.

[10] He went on to edit or publish several Kansas newspapers, including the Baldwin Ledger, the Ottawa Herald, and the Daily Republican, Republican-Journal and Irrigation Farmer, all in Salina.

[8][11] Bristow supported Benjamin Harrison for president in 1888, and that same year won election as secretary of the Kansas Republican Committee.

[13] Bristow campaigned for the Republican ticket of William McKinley and Garret Hobart in the 1896 United States presidential election.

[4] After McKinley took office as president, he appointed Bristow as Fourth Assistant United States Postmaster General.

[15][16] After the Spanish–American War, the McKinley administration dispatched Bristow to Havana to investigate and report on corruption in the postal service of the United States Military Government in Cuba.

[17] Bristow opposed the original version of the Mann–Elkins Act for regulating railroads and utilities, because he believed the proposed federal commerce court would weaken the Interstate Commerce Commission's authority, but supported the act when it was amended to place the proposed court's authority with the commission.

[18] Like most progressive Republicans, Bristow also opposed the Payne–Aldrich Tariff Act, which raised duties on imported products, arguing that manufacturers did not deserve to profit at the expense of higher prices for consumers.

[19] Bristow provoked a sarcastic comment from Vice President Thomas R. Marshall that has since become well known in American political lore.

[23] Marshall was preparing to smoke, and as Bristow approached, the following exchange took place:[23] In early 1915, columnist Thomas F. Logan repeated the story, though in his version some of the details had changed.

What this country really needs is a good five-cent cigar.”[23] In January 1915, Governor-elect Arthur Capper announced his intention to appoint Bristow to the Kansas Public Utilities Commission.