On February 17, 2015, Martinez Fischer was defeated in a special election by fellow Democratic House colleague Jose Menendez for the District 26 seat in the Texas Senate.

In a special runoff election marked by low turnout among Democratic voters and unprecedented participation by San Antonio Republicans, Menendez edged out Martinez Fischer.

[citation needed] Martinez Fischer challenged and lost again to Menendez for a full Senate term in the Democratic primary on March 1, 2016.

On June 27, 2014, while speaking at the Texas Democratic Convention, Martinez Fischer attacked the Republican Party, saying "GOP" should stand for "gringos y otros pendejos."

His office had also been handing out six Lotería cards to delegates, one depicting Republican gubernatorial candidate Greg Abbott as "El Diablito."