Editor's note: This story has been updated to reflect how Sen. Steve Daines plans to vote on the resolution.

As members of the U.S. House on Tuesday moved to block President Donald Trump's declaration of a national emergency, Sen. Jon Tester readied his own vote when the resolution comes to the Senate.

In a media call, Tester said he plans to vote for the resolution disapproving the president's national emergency, calling it an unconstitutional attack on the legislative branch of government.

“I think it's an attack on our Constitution, and certainly an attack on our legislative branch,” Tester said. “I think it's dangerous, not only from a constitutional standpoint, but from a precedent-setting standpoint.”

Tester served on a seven-member Senate committee that helped move Congress past last month's government shutdown by crafting and passing a bipartisan spending bill that included $1.37 billion for 55 miles of border fencing.

Trump signed the bill and simultaneously declared a national emergency, effectively bypassing Congress to grab additional funding to build 200 miles of border wall.

“We got together in a bicameral, bipartisan way on that conference committee, which I was a part of, and we were able to come up with an agreement,” Tester said. “The minute the president got the agreement, he said it wasn't good enough, and he decided to bypass Congress by using the emergency declaration.”

The president's declaration has set up a showdown with Congress and raised questions over the constitutionality of his action. The House, now led by Democrats, was expected to pass a measure Tuesday to roll back the president's declaration.

It would then go to the Senate, where it would only take a handful of Republicans to help pass it. Tester isn’t sure if the votes are there, but he doubts it would pass by a veto-proof margin.

“I don't know if there's enough votes to override a veto,” he said. “I don't know if there's 67, but there should be. It shouldn't be a political thing. This is a direct attack by the executive branch on the legislative branch. In normal days, regardless of party, that wouldn't be tolerated, but these aren't normal days.”

To help fund the wall, Trump plans to access around $3.6 billion in funding earmarked for military construction projects. Tester said that raises a number of questions, some of which land back in Montana.

Among them, Malmstrom Air Force Base was expecting replacements for its aging Huey helicopters and a new weapons storage facility needed to maintain its fleet of ICBMs.

“The president's emergency declaration to build a wall at the expense of our state's defense installations puts these projects at risk,” Tester said. “It raises many questions about the president's requests for more military funding only to steal it for political priorities.”

Tester said the additional funding sought by Trump in other coffers doesn't exist. He added that the $1.3 billion appropriated by Congress last fiscal year for the wall hasn't been spent, while this year's $1.37 billion isn't enough to satisfy Trump.

“A lot of the money he was going to draw on to build the wall simply doesn't exist, and there's all sorts of problems with that,” Tester said. “The vast majority of last year's $1.3 billion hasn't been spent.”

Sen. Steve Daines' office said the Montana Republican would vote in support of the president's emergency declaration.

"Last week, the senator traveled across Montana and heard directly from local law enforcement how Mexican meth is destroying Montana communities and families," Doyle said. "The illegal drug crisis is real, and securing the southern border will help protect Montana’s communities and families."