Experts tell senators Trump must demand North Korea's complete denuclearization Democrats pressed for congressional review of any deal with North Korea.

President Donald Trump said Tuesday that preparations for his June 12 summit with North Korean leader Jim Jong Un "are moving along very well."

"A lot of relationship being built," Trump told reporters at an event in the Oval Office. "A lot of negotiation going on even before the trip. But it looks like it's coming along fine. We'll see what happens. But very important. It will be a very important couple of days."

Earlier Tuesday, two foreign policy experts told senators on Capitol Hill that the United States must continue to demand total, verifiable denuclearization from North Korea.

“Complete denuclearization, which means dismantlement, removal of all fissile material, and production capacity must be the goal,” Amb. Joseph Y. Yun said in his opening statement before a Senate Foreign Relations subcommittee. “In order to get there, there must be concrete steps committed to by North Korea in the upcoming Singapore meeting.”

Yun previously served as the U.S. Special Representative for North Korea Policy and Deputy Assistant Secretary for Korea and Japan in the State Department’s Bureau of East Asian and Pacific Affairs.

“We must maintain the goal of complete denuclearization of North Korea,” agreed another expert on North Korea, Dr. Victor Cha. Cha, a Senior Adviser and Korea Chair for the Center for Strategic and International Studies, explained that “easing up on this goal...would have damaging effects regionally and globally.”

Several senators asked whether Congress should have a say in reviewing deals with North Korea if next week’s historic meeting between Trump and Kim succeeds.

Sen. Tim Kaine, a Virginia Democrat, noted that Congress mandated it review President Barack Obama’s efforts leading up to the Iran nuclear deal. Kaine questioned if similar protocols should be considered for any agreement with North Korea.

“Shouldn’t we have a uniform standard that the [potential] deal be subject to some congressional review?”

Yun responded that “any deal on North Korea” will have to lead to a “peace treaty.” Article II, section 2 of the U.S. Constitution grants the president the power to make a treaty “with the Advice and Consent of the Senate...provided two-thirds of the Senators present concur."

The former diplomat pointed to a “lack of congressional involvement” when it comes to North Korea.

“Practically nobody goes to North Korea,” Yun stated. He then stressed the need for more “dialogue.”

Maryland Democratic Sen. Ben Cardin noted that “Congress needs to be involved” in future talks with North Korea.

Later in the hearing, Sen. Chris Murphy, a Connecticut Democrat, asked Cha if he was concerned that President Trump’s advisors could theoretically use North Korea’s possible “failure to meet expectations...as an excuse to push early military intervention.”

“I’m not a lawyer,” Cha joked. Based on everything that the expert has heard, however, he responded that a “preventive military strike” requires congressional involvement.

Yun added that it would be “much more reassuring if...any military action be authorized by the Congress.”

“We’ve always considered military action,” Yun stated. “But we’ve always said it’s not worth another war on the Korean peninsula.”

After the hearing, Sen. James Risch, an Idaho Republican, told reporters about his communications with the White House and State Department in regards to the upcoming North Korea summit.

“The president, the vice president, and the secretary of state have all told me separately that their intent is to put together a treaty that will be submitted to the Senate under the Constitution for ratification,” he said.