President Donald Trump tempered his optimism on North Korea on Sunday, saying that “only time will tell” how things turn out, as U.S. lawmakers sounded skeptical about promises made by Pyongyang ahead of possible historic talks between the countries leaders.

“We are a long way from conclusion on North Korea, maybe things will work out, and maybe they won’t — only time will tell,” Trump said Sunday on Twitter. “But the work I am doing now should have been done a long time ago!”

In an earlier tweet, the president criticized NBC journalist Chuck Todd for suggesting that the U.S. had given ground to North Korea in negotiations. “Wow, we haven’t given up anything & they have agreed to denuclearization (so great for World), site closure, & no more testing!”

Sunday’s comments followed those from Trump on Friday after Kim pledged to halt nuclear testing in what was seen as a largely symbolic gesture aimed at softening the ground for talks between the two leaders. Trump then hailed “big progress” and said he looked forward to the summit with North Korea’s leader, which could go ahead in May or June.

Kim told a ruling party meeting in Pyongyang on Friday his regime would suspend tests of atomic bombs and intercontinental ballistic missiles after achieving its goal of building a nuclear arsenal, the official Korean Central News Agency reported. North Korea will shutter its Punggye-ri test site, a secluded mountain facility believed to be damaged after a hydrogen bomb test in September.

Bombs in Hand

However, the reclusive state’s media has steered clear of using the term “denuclearization” to describe Pyongyang’s offer. Kim has made no commitment to give up the estimated 60 nuclear bombs and the unknown number of intercontinental ballistic missiles he already has.

White House legislative director Marc Short said Sunday that the administration has “cautious optimism” about North Korea.

The ongoing negotiations with Pyongyang reinforce the need for a fast vote to confirm Mike Pompeo as the new U.S. Secretary of State, Short said on NBC’s “Meet the Press.”

Pompeo, in his role as CIA director, recently traveled to North Korea in secret to lay the groundwork for Trump’s potential meeting with Kim.

U.S. lawmakers sounded more skeptical than optimistic on Sunday.

Easily Reversible

On CNN’s “State of the Union,” Senator Bob Corker of Tennessee said Kim’s efforts should be met with caution. The Republican, who is chairman of the Senate Foreign Relations Committee, said North Korea’s leader has staged a “great public relations effort” to woo Trump.

Corker’s committee will vote Monday on Pompeo’s nomination, which would then move to the full Senate. The former Kansas lawmaker is nearing the votes he needs for confirmation after Democratic Senator Heidi Heitkamp of North Dakota said she’ll cross party lines to back him.

Senator Dianne Feinstein, a Democrat from California, termed North Korea’s pledge to suspend missile testing was “a beginning.”

“The question is whether it lasts or not,” Feinstein said on CBS News’s “Face the Nation.” “The reputation of the North Koreans has been that they don’t necessarily keep their agreements.”

Senator Tom Cotton, Republican of Arkansas and a close ally of Trump, said Friday’s announcement by North Korea was easily reversible. “It’s better than continued testing, but it’s not much better than that,” Cotton, a member of Senate’s intelligence and armed services committees, said on CBS.