Washington (CNN) Texas Democratic Rep. Vicente Gonzalez on Sunday flipped his support from Julián Castro to Joe Biden for the Democratic presidential nomination, saying now is the time to narrow the 2020 field and unite as Democrats.

Castro's "delivery could have been different," Gonzalez told CNN's Jake Tapper on "State of the Union," but the congressman said most of what he saw on the debate stage was "fair game in moving the process forward." Still, the Democratic Party needs to narrow the 20-person field to be successful, he said.

"We need to narrow the field and unite as Democrats to defeat (President Donald) Trump in November 2020. That's why I believe I'm moving my support to Vice President Joe Biden," Gonzalez, who represents the Texas 15th Congressional District, said.

Gonzalez called the former vice president a "steady ship" with White House experience who can defeat Trump. He called Castro, a former housing and urban development secretary under the Obama administration and former mayor of San Antonio, Texas, a qualified candidate, but said there are a number of qualified candidates.

Read More