Sen. Ron Johnson Ronald (Ron) Harold Johnson CIA found Putin 'probably directing' campaign against Biden: report This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda GOP set to release controversial Biden report MORE (R-Wis.) has expressed concerns about the precedent set by President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's national emergency declaration to reallocate funding for a border wall.

During an interview with Chuck Todd set to air in full Sunday on NBC's "Meet the Press," Johnson said he shared concerns from other GOP lawmakers that future presidents could follow Trump's example and declare emergencies to circumvent Congress.

“Absolutely I share those concerns which is why we’re going to take a very careful look at what he’s doing here in this instance,” Johnson said.

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He added that he was not sure if he would support a congressional resolution to disapprove of Trump's declaration.

“I’m going to take a look at it and I’ll decide when I actually have to vote on it,” Johnson said in a clip from the interview released Saturday. He added that he would have doubts about the president's declaration if he did not intend to rapidly use the money.

WATCH: @SenRonJohnson tells @chucktodd in an exclusive interview that he is concerned about Trump's national emergency declaration and the precedent it sets. But, Johnson has not yet decided if he would vote to disapprove of the president’s declaration. #MTP pic.twitter.com/SZC6bqTMZX — Meet the Press (@MeetThePress) February 16, 2019

Democrats are readying an aggressive response to Trump's decision Friday to declare a national emergency at the border, including potentially trying to block the move with legal action or legislation.

Reps. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezHouse passes bill to avert shutdown Trump attacks Omar for criticizing US: 'How did you do where you came from?' The Memo: Dems face balancing act on SCOTUS fight MORE (D-N.Y.) and Joaquin Castro Joaquin CastroHispanic Caucus members embark on 'virtual bus tour' with Biden campaign Hispanic caucus report takes stock of accomplishments with eye toward 2021 Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-Texas) said this week that they planned to introduce legislation to stop the emergency declaration. A Democratic aide said the pair was working to build support.

Trump on Friday declared an emergency to allocate additional money to build a barrier at the U.S.-Mexico border. The president made the announcement while saying that he would sign a bill to keep the government fully funded through the rest of the fiscal year.

The White House plans to redirect $3.6 billion in military construction funding toward the border project, and repurpose about $2.5 billion from the Defense Department’s drug-interdiction program and another $600 million from the Treasury Department’s asset-forfeiture fund through a separate executive action.

“I could do the wall over a long period of time. I didn’t need to do this, but I’d rather do it much faster,” Trump said when announcing his declaration Friday.

Critics immediately pounced on the comment, arguing it undermined the president's position that an emergency exists at the border. The White House later sought to clarify the remark.

Several groups have already said they would sue the president over the declaration.