Story highlights John McCain says the White House should have consulted with the Defense Department

The Arizona Republican said anyone who meets the military's standards should be allowed to serve

(CNN) Sen. John McCain said Thursday the White House is realizing it made a mistake when President Trump announced a ban preventing transgender Americans from serving in the armed forces without first consulting the military.

The decision, announced by Trump on Twitter Wednesday morning , reversed a policy initially approved by the Defense Department under President Barack Obama that would allow transgender people to openly serve in the military. The policy was still undergoing final review when Trump announced the decision to walk it back.

McCain said Thursday that Defense Secretary James Mattis, who last month told Congress he would take six more months to study the issue, was surprised by the announcement.

"I think they realize they made a mistake," McCain said. "I think generally speaking, it's accepted you consult the Secretary of Defense before you make a decision that has to do with defending the nation. Mattis was going through a study that they'd done for six months, and he had just extended."

"I know what Mattis said, that he wanted to complete the study, and he was surprised," McCain added.

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