In 1943, Mayor William D. Becker was killed in a glider crash at Lambert Airport in St. Louis.
Under the provisions of the city charter, Kaufmann, as President of the Board of Aldermen, became mayor for the remainder of Becker's term.
During his time as mayor, Kaufmann worked to pass a $69 million bond issue, which was approved by the voters in April 1944.
Kaufmann was unsuccessful in his efforts to get the Missouri Constitutional Convention to expand the boundaries of St. Louis City, which had been fixed in 1876.
He returned to his law practice and remained active in civic affairs.