President Donald Trumpís abrupt firing by tweet of Secretary of State Rex Tillerson on Tuesday triggered another round of chaos in an administration that appears more unstable than ever. Tillerson was a moderating voice and more in line with mainstream thinking on foreign policy than the president he irritated once too often, but he was a terrible fit for the job. CIA Director Mike Pompeo, Trumpís choice to succeed Tillerson, is more comfortable with the ways of Washington and this impetuous president.Trump and Tillerson never clicked, and the secretaryís support for the Iran nuclear deal and for the United States to remain in the Paris climate accord, along with reportedly calling Trump a moron, sealed his fate months ago. The former Exxon Mobil chief executiveís refusal to acknowledge the State Departmentís unique role in shaping Americaís relations overseas also left him with few supporters in the federal government and among Americaís allies. There was reason enough for Trump to fire him, but there was no reason to humiliate him, fire him on Twitter and then call him hours later from Air Force One.Pompeo has the presidentís ear, thanks to unflagging loyalty and tea party principles that align with Trumpís nationalist agenda. He is a hard-line former Republican House member who politicized the CIA, shares the presidentís unfortunate opposition to the Iran nuclear deal and questions whether the standoff with North Korea can be resolved with diplomacy. But he also has defended the intelligence communityís conclusion that Russia interfered with the 2016 election. Assuming he is confirmed by the Senate, Pompeo may be a secretary of state more in line with Trump on the wrong policy priorities ó but he also may reinvigorate the State Department bureaucracy and put diplomacy more at the forefront of Americaís global relations.Trump said Tuesday he made the change as part of preparing for his anticipated meeting with North Korean leader Kim Jong Un on a possible nuclear deal. Thatís his prerogative, and if this signals the presidentís intention to prepare seriously for these high-stakes talks, so much the better. It also should move the White House to fill key vacancies at the State Department that Tillerson had no use for, and it should give Americaís allies more confidence that greater weight is being placed on diplomacy in breaking the Korean impasse than on unpresidential taunts over who has the biggest nuclear button.But the United States faces a host of foreign policy challenges: curbing the nuclear ambitions of Iran and North Korea; fighting terrorism in the Mideast, Africa and Afghanistan; maintaining unity in Europe; dealing with the physical and economic impacts of climate change; and limiting the global fallout from Trumpís trade wars. These are just a few examples of why a healthy State Department, and a secretary of state who speaks with the authority of the president, are vital to U.S. national security.Tillerson was an adult in the room who was too often ignored and too often let his disdain for his boss show. Pompeoís better relationship with the president should make him a more effective emissary abroad. But he will need to balance the demands of staying in Trumpís graces with his larger obligation in this new Cabinet role to advance whatís best for the nation. He will be tested by an unsettled world and a mercurial boss, but global security still calls out for steady American leadership.