On Tuesday night, a few hours after President Trump's sudden announcement that he was firing FBI Director James Comey, a prominent Republican politician gave me this simple, blunt assessment of the Trump White House, "These guys scare me."

Trump's impulsive, vengeful decision to dump Comey has scared a lot of people. It suggests a pent-up anger and lack of judgment that would be worrisome in anyone, let alone the commander in chief. Worse, as has become too familiar with this White House, the decision to sack Comey was initially surrounded by a smokescreen of obfuscation that attributed the firing to Deputy Attorney General Rod Rosenstein, rather than Trump himself.

The Washington Post and The New York Times captured the pique that underlay Trump's decision to purge the FBI chief, which had been building since before the inauguration. The Times described Trump as brooding over "festering grievances" and "obsessed with loyalty." The Post said he was "increasingly agitated," with a "brewing personal animus" toward Comey, and "infuriated" that the FBI kept investigating Russia rather than chasing leaks.

Normally, it's wise not to overstate the importance of particular events. They're rarely as earth-shaking as they initially seem. But this may be one of those moments when the worst-case situation is actually happening: The president really did just fire the person who was running an investigation in which he is a possible target. How should conscientious citizens respond to that?

An Arab friend told me years ago that for every question, there is a right answer and a real answer. The right answer here is to trust in the rule of law and the institutions that maintain it. The American Constitution was designed to withstand political stress, and it has worked pretty well.

The real answer is that we depend, ultimately, on the political leaders who have taken an oath to uphold that Constitution. Otherwise, the vaunted institutions are just pieces of paper. Do our politicians and government officials have the guts to make hard decisions? Will they say no to improper orders and resign rather than carry them out? Can they escape the straitjacket of party loyalty?

The real answer, alas, is that we don't know. The Trump presidency is a test. We'll find out how strong our institutions are and, even more, whether this generation of leaders is worthy of our Founders. So far, the evidence is mixed. Trump still fires off such tweets as "The Russia-Trump collusion story is a total hoax," and many GOP officials give him a pass.

The first big test ahead is whether Rosenstein will call for the appointment of a special prosecutor to investigate the Russia matter. Given the way Rosenstein was used by Trump and Attorney General Jeff Sessions as cover for firing Comey, his credibility and reputation are at stake. Without a special prosecutor, much of the public will doubt that this is truly an independent investigation.

The White House should calm its jitters by remembering that this is a broad counterintelligence investigation of Russian efforts to influence the 2016 presidential election. Any examination of possible collusion with the Trump campaign would be "folded in" to that larger probe, stresses John Carlin, who oversaw the investigation as head of the Justice Department's national security division until last October, when he left to join Morrison & Foerster, a private law firm.

The second big test is the nomination of a new FBI director. Trump is certainly capable of making good decisions in the public interest: Look at his national security team of Defense Secretary James Mattis, Secretary of State Rex Tillerson, and national security adviser H.R. McMaster. He needs a similar pick for FBI director. "The FBI agents will be watching," Carlin told me. "They need to know that at the top of the chain, they're reporting to someone who shoots straight."

America has seen erratic presidential behavior before. Franklin Roosevelt's court-packing scheme was a reckless power grab. Harry Truman composed dark letters about his enemies, which he mostly didn't send, and ordered an illegal seizure of America's steel mills. Lyndon Johnson brooded obsessively about leaks and sometimes deceived and manipulated his friends and enemies alike. And of course, Richard Nixon bugged the Democratic National Committee and lied about it in the Watergate scandal.

Abuse of power isn't new. But America has survived intact because our institutions constrained presidential authority, and good men and women made sure the system worked. That's how we'll get out of this mess, too.

David Ignatius writes a foreign affairs column. He has also written eight spy novels. "Body of Lies" was made into a 2008 film starring Leonard DiCaprio and Russell Crowe. He began writing his column in 1998. To read more of his reports, Click Here Now.