Chris Christie endorses Donald Trump at a Texas campaign event (Tom Pennington/Getty Images)

Gov. Chris Christie was criticized on Sunday for his endorsement of Donald Trump and faced tough questions on ABC's This Week.

In a statement to NBC News, Meg Whitman, the national finance Co-chair for Christie's presidential campaign, called Christie's endorsement "an astonishing display of political opportunism."

The CEO of Hewlett-Packard took Christie to task for his about-face on Trump's ability to be president.

"Donald Trump is unfit to be president. He is a dishonest demagogue who plays to our worst fears. Trump would take America on a dangerous journey. Christie knows all that and indicated as much many times publicly," she wrote in a statement.

Christie endorsed Trump on Friday during a campaign event in Fort Worth.

"I've gotten to know all the people on that stage and there is none who is better prepared to provide America with the strong leadership that it needs both at home and around the world than Donald Trump," Christie said to the surprise of many

During an appearance on ABC This Week, Christie told host George Stephanopolous that he considers Whitman "a great friend" but they have a "difference of political opinion."

Stephanopolous challenged Christie on Trump's promise to build a wall between Mexico and the United States to keep immigrants from entering illegally, and on Trump's statements about Social Security reform, playing clips of Christie's own responses during the campaign. Christie said several times that he and Trump are not going to agree on every issue but they can have a discussion.

"This is the thing that I said and he will answer that question (about the wall)," Christie said. "But you know, to me, I'm not answering the question for him this morning."

Christie was steadfast in his statement that Trump is the best candidate to beat Hillary Clinton if she is the Democratic nominee.

"Donald Trump is going to be the Republican nominee for president of the United States. And he is going to bring this race to Hillary Clinton. He is the best candidate to beat Hillary Clinton in November and the best candidate to restore national security for our country," Christie said.

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