Some Senate Republicans are opposing President Donald Trump's suggestion that he may declare a national emergency to try to secure funding for a border wall.

While some of these senators support Trump's aim of building a wall on the southwestern US border, all have expressed concern about declaring a national emergency to fund its construction without congressional approval.

Trump has previously said there is a "good chance" he will decide to do this and has hinted at some kind of announcement during his State of the Union address on Tuesday night.

Sen. Lindsey Graham said there could be "war" within the GOP if Trump decides to declare a national emergency. Graham said he would be on Trump's side.

Some Republicans are worried that a national-emergency declaration would be defeated in court.

Democrats say they will "look at any legislative way to stop" such a declaration.

Some Senate Republicans are publicly opposing President Donald Trump's idea of declaring a national emergency to try to secure the border-wall funding.

Sen. Lindsey Graham has said it could expose divides so deep as to start a "war within the Republican Party" if Trump goes ahead.

At least eight GOP senators have publicly stated their opposition to such a move, in which Trump would aim to circumvent Congress to obtain funding for a wall along the southwestern US border.

Trump hinted on Friday that he could use Tuesday's State of the Union address to declare a national emergency.

He told reporters there was a "good chance" that he would declare a national emergency over the issue. "Well, I'm saying listen closely to the State of the Union," he said. "I think you'll find it very exciting."

When asked on Tuesday whether Trump would use the address to declare an emergency, the White House senior adviser Kellyanne Conway said Trump would rather Congress approve funding but had "an absolute right to do it."

Read more: Trump is teasing bombshells for his State of the Union address. They could include a national emergency over the wall and a new summit with Kim Jong Un.

"He wants Congress to finish its work and hopefully come to an agreement, put a deal on his desk that he will sign into law," she told reporters at the White House.

Graham, speaking in South Carolina on Monday, said he was "not optimistic" that the GOP could come to a border-wall-funding deal with Democrats. He said Trump would probably have to "go it alone" by declaring a national emergency, The Hill reported.

By Graham's own acknowledgment, this would most likely cause huge conflict within the party. "There could be a war within the Republican Party over the wall," he said.

Graham said he would "stand with" Trump if he decided to declare a national emergency, and he urged other Republicans to do the same and "get behind the president."

Sen. Lindsey Graham with journalists on January 24. Melina Mara/The Washington Post via Getty Images

Opposition from senators

But other GOP senators have signaled that they oppose declaring a national emergency, even if in principle they support building a border wall along the US-Mexico border.

Sen. Susan Collins of Maine said she was "in general opposed to the president using the national emergencies act," The Hill reported.

She said she believed it was "of dubious constitutionality" to use the act in this way and said she did not think "the intent was for it to be used in this kind situation."

Sen. Roy Blunt of Missouri said that he was "in favor" of Trump's proposed border wall but that when it came to declaring a national emergency, "I think it sets a dangerous precedent and I hope he doesn't do it," Politico reported.

Read more: Democrats unveiled a new border-security plan that still doesn't include money for Trump's wall but 'everything's on the table'

Sen. John Thune of South Dakota, the second-highest-ranking Republican in the Senate, said he and "a lot of my colleagues" had concerns about that strategy. "There's a lot of reservations in the conference about it and I hope they don't go down that path," he said, according to The Hill.

Sen. John Cornyn, left, with Sen. John Thune on Capitol Hill in 2017. Both senators have expressed concern about declaring a national emergency to secure border-wall funding. Aaron P. Bernstein/Getty Images

Sen. Richard Shelby of Alabama said he "wouldn't prefer" a national emergency over other ways to try to secure the funding, The Hill reported.

Sen. Thom Tillis of North Carolina said he would rather avoid a national emergency and was worried about giving the executive branch too much power, according to Politico.

Sen. Mitt Romney of Utah said he would rather "follow the legislative process to secure the border" in a "normal" way, according to Politico. He said he "will be studying" a vote to block Trump from moving forward with declaring a national emergency.

Sen. Mitt Romney with journalists on January 24. Romney said he would be "studying" a vote to block the president from declaring a national emergency. Melina Mara/The Washington Post via Getty Images

Some senators said they would not necessarily vote against declaring a national emergency but were still not convinced that doing so was the best strategy to get funding.

Sen. Ron Johnson of North Carolina said he wanted the Trump administration to "lay out the legal case" for a national emergency, according to Politico, but was "highly sympathetic" with Trump's desire to get the money.

Read more: Here's what would happen if Trump declared a national emergency to build his border wall

Sen. John Cornyn of Texas said that declaring a national emergency would be a "dangerous step" and warned that it would most likely end up facing numerous court challenges. "The president's going to get sued and it won't succeed in accomplishing his goal," he said, according to Politico.

Senate Majority Leader Mitch McConnell has privately cautioned Trump against using an emergency declaration as it could divide the Republican Party and may force Trump to issue his first veto, The Washington Post reported.

Legal challenges against declaring a national emergency

Experts are divided over whether it's legal for Trump to use a national-emergency declaration for a wall. If he does so, it is widely expected that he would face opposition in court, though such challenges could face their own roadblocks.

Trump talking to a Border Patrol agent while participating in a tour of US-Mexico border-wall prototypes. Kevin Lamarque/Reuters

Senate Minority Leader Chuck Schumer said he and House Speaker Nancy Pelosi would "look at any legislative way to stop" a national emergency declaration, The Hill reported.