After losing a campaign for Sheriff of Kings County (Brooklyn), Kline was elected as an Alderman for the 51st District in Brooklyn in 1903 and 1905, but lost re-election in 1907 due to Democratic redrawing of his district. He won back his seat in 1911 and became Vice-Chairman of the Board of Aldermen in 1912, promising to enforce all rules fairly from the chair (including those against smoking).[3]
When John P. Mitchel, the elected President of the Board of Aldermen, resigned in 1912 in order to become Collector of the Port of New York, Kline succeeded Mitchel. And when Mayor Gaynor (who had never fully recovered from an attempted assassination in 1910) died at sea in September 1913, Board President Kline became mayor.
He served out the remainder of Gaynor's term, leaving office on December 31, 1913. Despite his stated intention of keeping all the department heads appointed by his predecessor for the rest of his term, Kline, in his very last days of office, dismissed Rhinelander Waldo as Commissioner of Police rather than accept a New Year's Eve resignation.[4]
Although re-elected as alderman for his old district for the 1914–1915 term, Kline resigned in early January 1914 to begin four years as the City's Tax Commissioner for Brooklyn (reviewing appeals of property tax assessments).[5]
He is still (in early 2016) the only mayor of the consolidated (post-1897) city never to have won a citywide popular election to any office (such as those from which Joseph V. McKee and Vincent Impellitteri rose to become acting mayor). On the other hand, Kline is also the last serving or former mayor to win election to any other public office.
(1920 was a landslide election year for the Republicans under President Warren G. Harding, but in the statewide elections of 1922, without such a national race, the New York City Democrats Al Smith and Royal Copeland easily unseated Republican Governor Nathan L. Miller and Republican U.S. Senator William M. Calder.)[9]
^Tammany Gives Way To Fusion Aldermen; Dowling, the Retiring Leader, Says, However, He'll Have the Votes When Needed.The New York Times, Tuesday, January 2, 1912, page 20, retrieved on June 20, 2008. On taking office, Kline announced, "My rulings as Vice-Chairman, when I am called upon to occupy this chair in the absence of the President, will be fair, just, and equitable. I may make mistakes, but they will be mistakes of the head and not of the heart, and such mistakes may easily be rectified. I shall endeavor to maintain the dignity of this body, and I wish to state now that our rules must be enforced. There is a rule of this board that there shall be no smoking in this chamber. If you want smoking, adopt a rule to that effect; but don't put in a rule forbidding smoking and then expect the Chairman to close his eyes to that rule."
^Kline Ousts Waldo; Calls Him Childish; Willing to Break Down Police Department to Satisfy His Pique, Mayor Writes.The New York Times, Thursday, January 1, 1914, page 1, retrieved on June 20, 2008. "Rhinelander Waldo was summarily dismissed from office as Police Commissioner yesterday by Mayor Kline. The removal came as the climax of a series of complications that had kept the department in a turmoil ever since it became definitely known that Mayor-elect Mitchel intended to let Waldo go and appoint a Police Commissioner of his own choosing."
