In 1997, he was once again elected a deputy. He left New Space after personal differences with Carlos Raimundi, and in 1998 joined the Popular Socialist Party, remaining as vice-president of FrePaSo until 2000.<ref>Ex-canciller Caputo joins socialism, Clarín, 1998-02-13</ref> In 1999, he sought the FrePaSo nomination for election as Mayor of Buenos Aires, but lost to Aníbal Ibarra, who went on to win in 2000.
In 1997, he was once again elected a deputy. He left New Space after personal differences with Carlos Raimundi and joined the Popular Socialist Party, remaining as vice-president of FrePaSo until 2000. In 1999, he sought the FrePaSo nomination for election as Mayor of Buenos Aires, but lost to Aníbal Ibarra who went on to win in 2000.