Shortly after announcing a major shakeup on Twitter Tuesday, President Trump told reporters, "We're getting very close to having the Cabinet and other things that I want."

Trump wished outgoing Secretary of State Rex Tillerson well, but said he expects a more simpatico relationship with Mike Pompeo, the current CIA director whom the president has tapped to be the nation's top diplomat.

"We're always on the same wavelength," Trump said of Pompeo, whose confirmation hearing is expected in April. "We have a very similar thought process."

A White House official said Trump was eager to make the switch in advance of upcoming talks with North Korea and ongoing trade negotiations. Here are some areas where the change could make a difference:

North Korea

Tillerson was caught flat-footed last week when Trump abruptly accepted an invitation for face-to-face talks with North Korean leader Kim Jong Un. Tillerson, who was traveling in Africa, had told reporters just a day earlier that the U.S. was "a long ways from negotiations" with Pyongyang.

Trump acknowledged he hadn't discussed the idea in advance with Tillerson. "Rex wasn't, as you know, in this country," Trump told reporters on Tuesday. "I made that decision by myself."

Pompeo defended the president's move but stressed the U.S. and its allies will continue to press North Korea in advance of any Trump-Kim summit.

"This administration has its eyes wide open and the whole time this conversation takes place, the pressure will continue to mount on North Korea," Pompeo told CBS. "There is no relief in sight until the president gets the objective that he has set forth consistently during his entire time in office."

That objective is denuclearization. According to South Korean officials who met with Kim, the North Korean leader expressed a willingness to discuss it, though it's not clear exactly what that means.

Iran

Trump has threatened to tear up the Iran nuclear deal, negotiated by the Obama administration and five other countries, although so far he has stopped short of doing so. The deal gives Iran relief from certain international economic sanctions in exchange for suspension of its outlaw nuclear program. Tillerson and other national security advisers urged the president to move carefully in overturning the deal, arguing that despite Iran's other transgressions, the nuclear agreement is working.

This was one of the key differences Trump cited in explaining Tillerson's dismissal.

"We disagreed on things," Trump said Tuesday. "When you look at the Iran deal, I think it's terrible. I guess he thought it was OK. I wanted to either break it or do something, and he felt a little bit differently."

Pompeo, like the president, has been a fierce critic of the Iran deal, saying it doesn't go far enough in dismantling Tehran's nuclear program and that it's not permanent.

"President Trump is determined to prevent that from happening in North Korea," Pompeo told CBS. Trump's reluctance to live by the terms of the Iran agreement, however, may affect U.S. credibility in negotiations with Pyongyang.

Trade

Tillerson's ouster comes just days after Trump fired the opening salvo in what critics warn could become a trade war. The former Exxon Mobil CEO was among the advisers who reportedly tried unsuccessfully to stop the president from ordering steep tariffs on imported steel and aluminum.

Pompeo defended the president in an interview with Fox News Sunday, especially with regard to China, which is widely blamed for the glut of steel and aluminum on the world market.

"It was very clear that what the Chinese are doing, whether that'd be on trade or the theft of intellectual property or their continued advancement in East and South China Seas, this administration is prepared and engaged in pushing back against the Chinese threats so that we can have a good relationship with China in a way the world desperately needs," Pompeo said.

Chemistry

Trump told reporters Tuesday that he wished Tillerson well but conceded he and the former secretary of state often didn't see eye to eye. The president regularly undercut Tillerson, once tweeting that he was "wasting his time" in pursuing a diplomatic approach to North Korea.

Tillerson, in turn, made little effort to hide his disdain for the president. He pointedly did not deny an NBC report last October that he'd once called Trump a "moron."

Pompeo, who often delivers the president's intelligence briefing in person, enjoys a better relationship with Trump.

"For whatever reason, chemistry, whatever it is," Trump told reporters. "Right from the beginning, from day one, I've gotten along well with Mike Pompeo."

Former CIA Director Michael Hayden suggests that Trump and Pompeo share a similar worldview, which has pluses and minuses.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.