On March 20, 1916, Indiana governor Samuel M. Ralston appointed Taggart, his political ally, to the U.S. Senate to fill a seat left vacant by the death of Benjamin F. Shively. Taggart advocated efficient use of federal funds and opposed wasteful spending, although his time in the Senate was brief. That November proved a Republican sweep and Taggart lost the Senate seat to James E. Watson. In 1920 Taggart helped James M. Cox win the Democratic nomination in the presidential election. Cox reciprocated by supporting Taggart's challenge to regain the Senate seat from Watson, but again Republicans swept in the November general election: Warren G. Harding defeated Cox and Taggart lost to Watson.