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(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.

The switch of support comes days after Castro sharply criticized Biden – with an apparent jab at the former vice president’s memory – in a contentious moment dubbed “personal” and “not cool” by other candidates, but Gonzalez said that debate moment was not the reason behind his decision.

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.

“If you’re polling in the low single digits and you’re not raising resources, I mean it’s clearly a recipe for disaster,” Gonzalez said.

In response to the pulled endorsement, Castro campaign spokesman Sawyer Hackett said, “Congressman González is entitled to endorse whichever candidate he feels represents his values. Secretary Castro will continue to fight for a better future for all Americans, including a health care system that ensures all Americans have access to quality coverage.”

During the third Democratic presidential debate in Houston and hosted by ABC News Thursday, Castro sharply accused the former vice president of forgetting what he’d said just minutes before during a disagreement over a minor point in the candidates’ broader discussion of whether to embrace “Medicare for All,” which Biden has opposed.

“Are you forgetting what you said two minutes ago?” Castro said to Biden. “Are you forgetting what you said two minutes ago? I can’t believe that you said – two minutes ago – that they had to buy in and now you’re forgetting that. We need a health care system where you’re automatically enrolled.”

The congressman said he recently met with Biden and said he is in “great health” and “mentally sharp.” He said Biden is “a lot healthier than Donald Trump.”

The 76-year-old Biden along with two of his Democratic challengers – Vermont Sen. Bernie Sanders, 78, and Massachusetts Sen. Elizabeth Warren, 70 – have pledged to release their medical records before the Iowa caucuses. Trump, 73, was the oldest president at the beginning of his first term in 2017.

Gonzalez told Tapper that “people make mistakes” and “misspeak,” adding: “But for the most part, (Biden)’s sharp, he’s on target, when you meet with him personally he’s clearly in physically good shape.”

CNN’s Polson Kanneth contributed to this report.