It has before. Following Obama's logic, Attorney General Janet Reno and her deputy, Jamie Gorelick, ruled that evidence seized in an immigration prosecution couldn't be turned over to intelligence operatives investigating terrorism.
The "Gorelick Wall" barred anti-terror investigators from accessing the computer of Zacarias Moussaoui, the 20th hijacker, already in custody on an immigration violation.
He was taking flying lessons in Minneapolis at the time, so we wondered what he was up to. But we didn't look at his computer, and find the e-mail addresses and records of fund-transfers to each of the 9/11 hijackers - information that might well have prevented the attacks.
Our constitutional protections are wonderful and shouldn't be abridged on any account. But the protections in the Fourth, Fifth and Sixth Amendments relate to prosecution under criminal law.
Intelligence that doesn't lead to prosecution isn't covered. But Obama would cover it anyway. He'd require us all to proceed in the way we had to in the halcyon days after the 1993 World Trade Center bombing - procedures that led us to miss the point of what was going on, to fail to identify the real culprits until it was too late and left us unprepared for future attacks.