(CNN) - Republican defense hawks are watching closely as President Donald Trump prepares to meet with North Korean leader Kim Jong Un, an unprecedented meeting that could redefine the future of US and North Korean relations for decades to come.
On Thursday, South Korea's national security adviser Chung Eui-yong delivered the invitation to Trump along with a message that North Korea would be willing to discuss their nuclear program. Soon after, the White House announced Trump would be willing to sit down with Kim.
But on Capitol Hill, the reviews from defense hawks were cautious, mixed and in some cases non-existent. After a year of tough talk, Trump, who before entering the White House had little foreign policy experience, will be sitting down in one of the most politically fraught discussions of his presidency and some hawks warn Trump needs ground rules first.
"#NorthKoreaTalks would actually be harmful unless it is clear beforehand to them & world that 3 items are non-negotiable. We will not abandon #SouthKorea we will never accept #NorthKorea as legitimate nuke weapon power & missiles that can strike U.S. will not go unchallenged," Sen. Marco Rubio, a Florida Republican and member of the Senate Foreign Relations Committee, tweeted Friday.
Some Republicans have argued that Trump himself was to credit for the recent breakthrough with Pyongyang even if they urged caution.
"While US policy toward North Korea has failed for decades, it is clear that a series of sanctions recently put in place by Congress and the administration are having a real impact," Senate Foreign Relations Committee Chairman Bob Corker, R-Tennessee, said in a statement. "As the administration begins to work through the important details of such a meeting, we must continue to apply maximum pressure to the regime in Pyongyang. Skepticism and caution are critical as these discussions continue."
One of the Senate's top defense hawks, Arkansas Sen. Tom Cotton, also urged skepticism in a statement Friday afternoon.
"The patterns of U.S.-North Korea crises are well-worn and North Korea's nuclear and missile capabilities are obvious," wrote Cotton, an Army combat veteran who has advised the White House on foreign policy issues like Iran. "A summit could possibly break those patterns and lead to the peaceful denuclearization of the Korean Peninsula. But we must remain deeply skeptical of North Korea's intentions and under no circumstances should the United States and our allies grant unilateral concessions."
Some top Republicans have yet to react to the news on North Korea. Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan did not issue official statements on the news.
Experts have warned that the talks between Trump and North Korea are high stakes and unprecedented in many ways. Unlike past high-profile meetings between US presidents and foreign leaders, the North Korea meeting was announced before many pertinent details surrounding the talks were ironed out or before any public lower-level diplomat discussions were established.
"I think everyone is surprised," said Ivo Daalder, president of the Chicago Council on Global Affairs and former US ambassador to NATO. "I'd say shocked by the speed at which this is happening."
Daalder warned that preparing for the meeting will take "extraordinarily hard work."
"This is serious stuff," he said. "We are not doing a real estate deal here we are dealing with a country that has dozens of nuclear weapons."
On Friday, the White House warned that the meeting would not take place unless they saw some "concrete" actions from North Korea first.
"We're not going to have this meeting take place until we see concrete actions," White House press secretary Sarah Sanders said. "We have to see concrete and verifiable actions take place."
Sanders suggested North Korea would need to take steps toward denuclearizing, though North Korea has not made any commitment to do that before talks take place.
"We feel very confident in where we are," Sanders said during the White House briefing Friday afternoon.
Some Republicans have expressed confidence in Trump's ability to negotiate, however, even as they continue to voice their skepticism that the meeting may be fruitless.
"After numerous discussions with President Trump, I firmly believe his strong stand against North Korea and its nuclear aggression gives us the best hope in decades to resolve this threat peacefully," South Carolina Sen. Lindsey Graham said in a statement. "I am not naïve. I understand that if the past is an indication of the future, North Korea will be all talk and no action. However, I do believe that North Korea now believes President Trump will use military force if he has to."
While some Republican hawks were open to Trump's negotiations, they weren't alone. Sen. Tammy Duckworth, a Democrat from Illinois, said she welcomed Trump's "embrace of diplomacy" even as she offered a strong warning.
"I welcome the President's new embrace of diplomacy over his prior reckless bluster," said Duckworth, also an Army combat veteran. "However, I would strongly urge the administration to remember that Kim Jong Un, like his father and grandfather before him, have long sought a visit from the President of the United States to enhance their own prestige and justify their dangerous pursuit of nuclear weapons."
She suggested the White House should nominate an ambassador to South Korea and added that accepting such an invitation "carries tremendous risk."
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