The chairman said "nobody should be too surprised," however, that Trump intends to redirect the money, considering congressional Democrats agreed to forgo a ban on that kind of reprogramming in the funding bills Trump signed in late December.

Republicans in both the House and Senate have already been forced to vote twice over the last year to overturn Trump’s previous emergency order to shift $3.6 billion in military construction funds toward the border wall. While the president promptly vetoed those rebukes, the votes caused discomfort for GOP lawmakers torn between supporting Trump and delaying projects that benefit military families in their home states.

“I wish they’d get the money somewhere else, instead of defense," Senate Appropriations Chairman Richard Shelby (R-Ala.) said. | Zach Gibson/Getty Images

Eleven GOP senators joined with Democrats in September to disapprove of the president's last declaration. Sen. Lamar Alexander (R-Tenn.), who was among those who supported the rebuke, said Tuesday that he would once again vote to spike Trump’s emergency edict if the question comes to the floor a third time.

Alexander, who is retiring at the end of his term this year, said the president “should not spend money that Congress hasn’t appropriated using the emergency authority.“

“The separation of powers is the principle guarantee of our liberty," he said. "And it’s important to observe it and respect it."

Sen. Patrick Leahy (Vt.), ranking Democrat on the Senate spending panel, said he expects even more Republicans might vote to rebuff Trump's latest plan to shift $7.2 billion.

“You’d think they would be on board now,“ Leahy said of Republican lawmakers. “It’s bullshit to say: Let the White House do whatever they want.”

The ranking member said Trump’s plan amounts to “one more example of saying: ‘We don’t care what the Congress does. We’ll steal money from everything ... to build a wall that can be scaled or sawed through with a $100 device that you can buy at a hardware store.’”

Sen. John Cornyn (R-Texas), a close ally to Majority Leader Mitch McConnell, called Trump’s reported plan an “unfortunate outcome" but blamed Democrats for their unwillingness to fund the border wall to the president's liking.

“I wish it wasn’t necessary,” the former majority whip said. “The problem is, Congress has failed to appropriate adequate funds for border security, which is the reason his hand was forced."

In the House, top appropriators said another multibillion-dollar shift toward the border wall would fly in the face of congressional spending authority.

The reprogramming would “do further violence to the Constitutional separation of powers that are inherent to our democracy," House Appropriations Chairwoman Nita Lowey (D-N.Y.) said in a statement Tuesday, along with Defense Appropriations Subcommittee Chairman Pete Visclosky (D-Ind.) and Rep. Debbie Wasserman Schultz (D-Fla.), who chairs the spending subcommittee that funds the Department of Veterans Affairs and military construction projects.

If the president follows through, the House appropriators said, the move would also be “forcing service members and their families to pay for his wall” and would be “stealing funding that was intended for meaningful counter-drug priorities” in the midst of a national opioid addiction epidemic.