Former homeland security adviser Tom Bossert said Sunday that he doesn't believe 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's executive order ending family separations will "survive three weeks."

The ex-Trump administration official told ABC's "This Week" that the order, which Trump signed last Wednesday, runs up against a 2015 ruling from a judge who said that even detaining families together was inhumane.

"This executive order the president put out to try to fix this problem is going to run headlong into the 9th Circuit judge that decided in 2015 that even detaining with parents is inhumane," Bossert said. "She called President Obama's policy of detaining children and parents together inhumane."

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"There is no way this executive order survives first contact, because her view of President Trump will be harsher," he continued.

Trump signed the executive order amid intensifying backlash over his administration's "zero tolerance" policy. The policy aims to aggressively prosecute migrants who cross the southern border into the U.S. illegally, but quickly drew fire across party lines for separating thousands of migrant families.

The order allows most families to be detained together, though, under current law, the federal government is barred from keeping children in immigration detention centers for more than 20 days.

Republican lawmakers are reportedly preparing to vote on a narrow immigration bill that would allow migrant children to stay in detention centers with their parents for longer than 20 days.

The news comes days after the Justice Department asked a federal district court to modify the 20-day limit, known as the Flores settlement.