Immediately after his departure from government, Dehler was elected chairman of FDP's parliamentary group and of the federal party, replacing Hermann Schäfer and Vice-Chancellor Franz Blücher, respectively.
It was in 1956 as well that Dehler made his decisive move against Adenauer: On 23 September 1956, just a year before the next federal elections, the FDP parliamentary group in the Bundestag decided to leave the coalition with CDU/CSU.