President Harry Truman established the CIA in 1947 to prevent future Pearl Harbors and to deal with the developing threats of the Cold War.

He did not know this espionage agency would later topple foreign governments, assassinate people, operate overseas torture camps, and frustrate virtually every president who came after him.

America has always had spies going back to George Washington’s revolutionary efforts just as political leaders have engaged in espionage going back to ancient China and Greece.

Most Americans are understandably confused about the role of the CIA. We wish we lived in a world that didn’t need such an agency, yet most would reluctantly agree with Machiavelli who, way back in 1513, wrote that “men who want to act virtuously in every way necessarily come to grief among so many who are not virtuous.”

Retired CIA officers say that “like war, spying is a dirty business,” yet just as a soldier’s job in war is to kill, spies and covert operatives are expected to capture enemy secrets and disrupt nefarious enemy operations.

U.S. Secretary of State Henry Kissinger, adviser to several presidents, said “covert operations should not be confused with missionary work.” Former CIA Director Michael Hayden adds that “covert actions are always on the edge. They take place in a gray area — gray ethically, gray legally, gray operationally — they’re always out there on the outer edge of executive prerogative.”

Presidents have been challenged as they try to supervise the ever-growing and largely secretive CIA — which is now just one of 18 federal intelligence bureaucracies.

One of President John F. Kennedy’s worst decisions was going along with a CIA planned invasion of Cuba. He apologized to the nation and took responsibility but never trusted that agency again. President George W. Bush relied on CIA information about Iraq that proved to be wrong, and he later had to apologize for allowing the CIA to operate torture camps in Thailand, Poland and elsewhere.

President Donald Trump believes the CIA is the capital of the deep state. He has said he thinks the CIA was probably behind President Kennedy’s assassination, and he has faulted CIA intelligence on Russia and Iran. He says he is cutting personnel in the intelligence agencies, but he has authorized expanded covert cyber operations.

Those who want a deeper understanding of the CIA’s mission and its successes and failures should read a new book by Pulitzer Prize- and National Book Award-winning Tim Weiner, “The Mission: The CIA in the 21st Century.” This is a likely bestseller and will be carefully dissected by intelligence operatives around the world.

Weiner’s book admires many of the people at CIA and rightly notes that most of its successes go largely unnoted and underappreciated. He suggests the CIA played a major positive role in ending the Soviet Union, bringing an end to Libyan leader Moammar Gadhafi’s nuclear weapons program and alerting the United States and NATO of Russian President Vladimir Putin’s plans to invade Ukraine.

Weiner mentions other successes, as well. He salutes many courageous and dedicated analysts and counter-terrorists who have served our country.

Yet his book, building on decades of investigative reporting and interviewing about 100 former CIA officials, is generally critical of presidents and the CIA.

Most presidents have tried to “reform” the CIA, strengthening its effectiveness and increasing its accountability to the White House and Congress. Yet, presidents learn that dealing with Russian and Chinese spies and hackers can be risky, expensive and frustrating.

Weiner’s excellent book shares several stories where CIA operations either backfired or violated the agency’s charter and constitutional precepts. Thus, it has spied on American citizens, killed American citizens, operated facilities that relied on torture, waterboarding and sadistic enhanced-interrogation procedures that presidents have had to apologize for — and for which the agency has been reprimanded.

The CIA also has occasionally collaborated with drug dealers, mobsters and unsavory assets and operatives.

Some writers suggest that it is OK, at least on occasion, to walk with the devil until you have crossed the bridge. Yet Weiner asks whether people in the White House or our intelligence agencies understand where to draw the line, legally and morally.

Weiner quotes a senior counterintelligence official who is religiously devout as saying, “I spent my entire CIA career lying, cheating, stealing, manipulating, deceiving …” Such officers often believe in theories that that it is morally sound for a soldier to kill in a “just” war; therefore, it is equally permissible for CIA agents to do their work.

As one put it, “If we’re going to defend our country against the evils that are out there, we can’t go out there with our hands tied behind our back. We’ve got to fight tough …”

The question is: How tough is too tough? When do CIA agents cross the line?

Weiner raises questions about whether any of us know whether what we are doing may betray the basic values we are fighting for.

He also asks, “what if an American president with authoritarian tendencies asks the CIA and other intelligence organizations to spy on domestic political rivals and American citizens?”

Readers may be surprised that Weiner suggests that, “The officers of the CIA would be the only line of resistance. Unless they rebelled against him, the CIA would no longer be an intelligence service under the law, but a secret weapon wielded by a man above it.”

For those who want an instructive short course on the CIA, here are other books, a novel and three movies that splendidly supplement Weiner’s “The Mission”:

1. Allen W. Dulles, “The Craft of Intelligence” (Roman & Littlefield, 2016). A history of the CIA’s founding and initial missions — insightful and self-serving accounts by one its famous directors.

2. Henry A. Crumpton, “The Art of Intelligence” (Penguin, 2012). Instructive accounts of how to recruit foreign assets and engage in clandestine counterterrorism by a justly admired CIA leader.

3. Norman Mailer, “Harlot’s Ghost” (Random House, 1991). Prize-winning leftist writer gave us an overly long and convoluted yet brilliant fictionalized account of the CIA’s political and operational culture in the 1950s and 1960s. CIA officers questioned some of its exaggerations yet loved it.

4 “Charlie Wilson’s War “(2007). An Aaron Sorkin-directed movie starring Tom Hanks. It tells how a Texas congressman teamed up with CIA to wage a successful, largely secret war helping the Mujahedeen in Afghanistan oust the Soviet Union in the 1980s.

5. “Zero Dark Thirty” (2017). A haunting and disturbing thriller depicting a dogged CIA operative (played by Jessica Chastain) who “does what it takes” to obtain information that led to the capture of Osama bin Laden. The film suggests her efforts were key to his capture. CIA brass downplayed the movie’s narrative, saying this was just one of many factors. The movie was a box-office hit.

6. “The Report” (2019). This was a low-budget box-office failure. But it is an important film sharing the painstaking investigation by the U.S. Senate into unauthorized CIA torture activities during the George W. Bush administration. The CIA hated this investigation, tried to undermine it and has succeeded in preventing the final Senate report from being publicly released. Actor Adam Driver does a fine job, and the movie raises tough questions.

Read these books and view these films, then ask: What type of intelligence agencies do we want, do we need? And how do we ensure they serve the best interests of the American people and the American Experiment?