Originally Published: 04 JUN 22 15:03 ET

Updated: 27 JUN 22 10:47 ET

By Janelle Davis, CNN

(CNN) -- Their mission was to break into the Democratic National Committee headquarters in Washington, bug the room and photograph documents. If everything had gone as planned, no one would have ever known.

But instead June 17, 1972, became an infamous day. The burglary set off a series of actions that brought down Republican President Richard Nixon -- the only US president to resign.

"Watergate is the largest political scandal in American history," John Dean, who was White House counsel to Nixon, told CNN for the Original Series "Watergate: Blueprint for a Scandal," which commemorates its 50th anniversary.

The break-in and subsequent cover-up forever changed American politics, and "Watergate" became a synonym for government corruption. The crime is still referenced in today's political discourse, as with Bridgegate, Pizzagate and Deflategate.

Here are six mistakes that led to the Watergate investigation -- the first dominoes to fall in the political scandal.

They used the 'F-team'

While president, Nixon created a White House unit called the "plumbers." This unit had two goals: investigate leaks of sensitive information and discredit the administration's enemies.

Since the President couldn't use official organizations like the FBI and the CIA for these illegal activities, Nixon's White House used what Tim Naftali, CNN presidential historian and director of New York University's undergraduate public policy major, calls "a ragtag group."

"The country was very fortunate that the CIA and FBI refused to bend completely to Nixon's will, so Nixon and his lieutenants opted to go outside the established institutions to do their dirty work," he said.

In 1971, the plumbers broke into the psychiatrist's office of military analyst Daniel Ellsberg to photograph the psychiatrist's notes on Ellsberg try to smear him in the press. Ellsberg was a target for leaking the Pentagon Papers -- a top-secret multi-volume report that revealed senior American leaders knew that the Vietnam War was unwinnable.

The plumbers' objective was to enter the office and leave undetected. But they couldn't open the door, which they had secretly left unlocked earlier in the day, so they broke a window, creating a scene. Then they didn't find any psychiatrist notes, so they left empty-handed.

"So you'd think that would be the end of them, but it wasn't. The same group gets reconstituted," Naftali said. For Watergate, "the leadership is the same and the bulk of the team is the same."

"It wasn't like the White House is relying on the A-team; they are relying on the F-team," he said. "So it's not surprising they bungled it."

Failed attempts raised the stakes

The five men tasked with breaking into the DNC made multiple attempts at the task. The more attempts, the more likely you're going to get caught.

"The first time they failed completely because the door was locked and they didn't have the right locksmith with them," Naftali said.

"The second time they didn't appear to know where Larry O'Brien's office was located," Dean explained. O'Brien was the campaign chairman for Democratic Sen. George McGovern, who was running for president against Nixon in 1972. "So they bugged an empty conference room."

The third attempt was intended to correct the previous errors. But the third time was not the charm.

"They wanted to move a bug. They had three more bugs, which they wanted to plant. They were also going to put a listening device in a smoke detector," Naftali said. "This would have been a massive espionage operation had it succeeded."

Afterward, Dean recalled Gordon Liddy, the organizer of the Watergate break-in and a former special agent of the FBI, saying to him: "'I shouldn't have had so many people. But we had to get back in there. ... I know I've screwed up terribly, and I can understand if you want to take me out."

Taped door latch was discovered

A simple mistake by James McCord, a former CIA officer who was one of the burglars, led to a watchman foiling the crime of the century.

"McCord was the wiretapping expert on the team," Naftali said. "And he insisted on taping the doors. And he was asked, did you remember to remove all the tape? And he said yes. And he hadn't."

The crew had placed tape over every door latch -- to prevent the self-locking doors from engaging -- from the basement to the sixth floor, where the DNC offices were.

Watergate security guard Frank Wills spotted the tape plastered over one door's latch. He called the police at 1:47 a.m. and reported the break-in.

Years later, one of the burglars, Eugenio Martinez, told Naftali in an oral history for the Nixon Library that he had been surprised by all the mistakes and that the tradecraft errors were difficult to understand.

The miscommunication

A backup plan was in place in case police were notified, but that was also botched.

A lookout man, Alfred C. Baldwin, was across the street with a walkie-talkie to alert the burglars if anyone was coming.

Naftali said, "McCord turned down the volume on the walkie-talkie. So when the lookout man could see DC police moving towards DNC headquarters, the burglars didn't get the alert."

When Baldwin finally was able to notify the crew, it was too late: Police were already in the building. They spotted the five men, who were all wearing surgical gloves, crouching behind desks.

The burglars didn't dress like burglars

After the men were taken into custody, Ron Ziegler, the White House press secretary, downplayed the break-in as a "third-rate burglary."

The journalists assigned to cover the arraignment assumed it was a non-story. Journalist Lesley Stahl joked to CNN that it initially appeared to be a "nothing burger" and said she had gotten the assignment because the editor gave the story to "the new girl."

But quickly, the signs that this story was significant were hard to ignore.

The five intruders -- Bernard Barker, Virgilio Gonzalez, Frank Sturgis, Martinez and McCord -- appeared in court hours after the arrest dressed in business suits.

"Nine months on the police beat, I'd never seen a burglar who was well dressed," journalist Bob Woodward, who covered Watergate for The Washington Post, told CNN.

What police discovered in the men's possession made them even more suspicious. The men had hundred-dollar bills (with the serial numbers in sequence), lockpicks, door jimmies, cameras, a short-wave receiver that could pick up police calls and three pen-sized tear gas guns, the Post reported in 1972.

"When the DC police caught them, they had something like 35 rolls of undeveloped film and very advanced cameras with them. So they weren't just looking for one file. They were looking for tons of information," Naftali said.

Stahl said that's when she knew this wasn't just a local break-in. It was something much bigger.

"I was getting more and more excited about this story," she said. "This was going to go higher."

The 'holy s*' moment

Without a backup plan in case of an arrest, the burglars were cornered into revealing some key information that morning in the courtroom: three key letters, to be exact.

Woodward recalls the jaw-dropping moment when one of the suspects was questioned: "The judge said, 'Where have you worked?' And the lead burglar, McCord, said 'CIA.' And when he said CIA, I think I blurted out, 'Holy s*.' "

"Bob's reaction was the right one: Holy s*," journalist Carl Bernstein, who worked with Woodward to uncover the Watergate scandal, told CNN.

"CIA. Oh my goodness, OK. We're in a whole new territory," said Stahl.

McCord had retired from the CIA and was a security officer on Nixon's Committee to Re-elect the President. The others had been hired by Nixon campaign aides: Liddy and Howard Hunt, a former CIA officer and counsel to the campaign committee.

"The White House understands immediately that this could lead back to them," Naftali said.

In the months that followed, FBI agents, journalists and congressional investigations began to piece together details of the scandal that pointed to White House involvement.

"Watergate is not the story of one break-in. It's the story of a pattern of presidential betrayal of trust," concluded Naftali. "What's really troubling about this story is if Nixon had chosen more professional secret warriors, think of the damage that could have been done to our democracy."