Washington (CNN) A Republican senator warned on Sunday that if President Donald Trump declares a national emergency on the southern border in order to fund the construction of a border wall, the move is "going to go to court and the wall won't get built."

"I would hate to see it. Using that act, it would be -- in this instance, it would be a far larger act than has ever occurred in the past, so I'd prefer not. Primarily because if we do that, it's going to go to court and the wall won't get built," Sen. Ron Johnson of Wisconsin told CNN's Jake Tapper on "State of the Union."

Instead, Johnson said, Trump and congressional Republicans should "keep pressure on Democrats to actually come to the negotiating table in good faith and fund what they've supported in the past."

Congressional Democrats are engaged in a more than three-week battle with Senate Republicans and the White House over funding for a wall along the southern border. Trump has been mulling the use of a national emergency to fund the project, saying last week that he was nearing a decision on the matter and that he would take the step -- which would likely be subject to an immediate legal challenge -- if talks with Democrats continue to go nowhere.

Sen. Lindsey Graham, R-South Carolina, said Sunday that Trump told him earlier in the day that he's still considering using his emergency powers to secure funding for the wall.

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