More than one-third of the money President Donald Trump wants to redirect from other federal programs to build a border barrier is likely to be unavailable from the sources he has identified.

As a result, it may be difficult for the president to circumvent Congress, even if a resolution disapproving of his “emergency” moves is never enacted.

Trump announced Feb. 15 that, using emergency powers, he wants to divert as much as $6.7 billion from other programs to finance the construction of barriers along the U.S.-Mexico border. That includes $3.6 billion from unspent military construction money, $2.5 billion in unspent Pentagon counterdrug funds and $600 million from a Treasury Department asset forfeiture account.

But the Defense Department has told lawmakers that only $85 million remains unspent in the counterdrug account, a House Appropriations spokesman said Thursday.

The Pentagon is planning to ask Congress for authority to reprogram more than $2.4 billion from other military programs into the counterdrug account in order to then take it right back out and move it to the wall project.

“The Department would need to reprogram additional funding into the account to reach the up to $2.5 billion that may be required for border security support,” said Christopher Sherwood, a Defense Department spokesman.

Flashback: Trump announces national emergency on border, despite likely legal challenge

However, a reprogramming request must be approved by both Republicans and Democrats on the four authorizing and appropriating panels that oversee the Pentagon.

Such approval in this case is all but certain to fail. All it would take is one chairman or ranking member to say no.

On Thursday, one of those lawmakers, Indiana Democrat Peter J. Visclosky, chairman of the House Defense Appropriations Subcommittee, said in a statement that he would turn down any request to reprogram military money to pay for a border wall.

“I am adamantly opposed to the use of any funds provided by Congress to the Department of Defense for the unauthorized construction of a wall on the Southwest border,” Visclosky said. “I and the other members of the House Appropriations Committee will carefully examine each element of the President’s proposal and the serious jurisdictional and Constitutional concerns that it raises.”

The $2.5 billion comprises about 37 percent of the money Trump wants to redirect to the border initiative and away from its congressionally approved purposes.

Trump could still find other ways to pay for the project against Congress’ wishes, including adding to the amount of military construction money he will tap. According to a House Appropriations Committee spreadsheet, there appears to be some billions of dollars in previously appropriated but unobligated military construction money that could be available to be redirected from the projects the military and Congress approved.

The Pentagon has yet to announce which military construction projects it will tap to bankroll this year’s installment of wall money.

The additional border barriers could eventually cost an estimated $25 billion.

Some on Capitol Hill say they are bracing for another possibility: that the president could move money as he wishes in the Pentagon budget and just disregard the traditional requirement that a president must get congressional approval for shifting sizable amounts of money from one account to another.