Former Housing and Urban Development Secretary Julián Castro said Sunday that President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE is "not behaving like he's fit for office."

"'He's not giving the American people or our allies around the world any sense that there's a rationale for the decisions that he's making. And the events of this last week were just another example of that, whether it's a sudden announcement of a withdrawal in Syria or the turmoil with his staff," Castro said on NBC's "Meet the Press."

Castro's comments came following a week in which Trump announced he would withdraw U.S. troops from Syria, prompting the resignation of Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE.

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Castro, who is considering a bid for the presidency in 2020, added that Trump is "just so erratic."

"And so I think that, what you're seeing around the country is that people who voted for him have begun to reassess him," Castro said. "And folks understand that we need different leadership. And the sooner we get that, the better."

Castro also said that "many folks recognize that it was time for us to pull out of Syria," though he added that Trump should have had a better plan for withdrawing troops.

"For our own sake, for the sake of our troops, for the sake of our allies, once you're there, you have to actually have a solid plan for how you're going to withdraw. And what we saw this week is not the way that it should be done by a president," he said.