Former U.S. Rep. Francisco "Quico" Canseco, a Republican, is challenging U.S. Rep. Joaquin Castro, a San Antonio Democrat, in 2018.

Canseco filed paperwork Monday with the Federal Election Commission to run as a Republican for Texas' 20th Congressional District, which Castro has represented since 2013. In an interview, Canseco said he spent the summer traveling the district and heard from people who want "somebody who has their back."

"I think that one issue that is very lacking is that person-to-person representation and making sure that the needs of an urban district are being met and not just the people who will ultimately vote for him in very thinly participated elections," Canseco said.

The 20th District is heavily Democratic, and Castro easily won re-election in 2014 and 2016. Republicans did not field a candidate against him in either election.

Castro has said he plans to run for another term in 2018, despite encouragement to seek statewide office — potentially the governorship.

Canseco represented Texas' 23rd Congressional District, the most competitive in the state, from 2011 to 2013. He was unseated in 2012 by Democrat Pete Gallego, who held on to the district for one term before losing it to the current representative, Republican Will Hurd.