Why does the US government let millions of people access its secrets?

John Cohen had spent 32 years in law enforcement and national security, ultimately taking over the Office of Intelligence and Analysis at the Department of Homeland Security, where he worked every day to make sure authorities across the country were aware of the greatest threats facing their communities. His government work required him to have a top security clearance.

But when he decided to leave government four years ago, he got to keep his clearance -- a privilege he says "absolutely" helped keep Americans safe.

At the time, the nation was facing what Cohen would only describe as "a specific threat issue," and thanks to his continued clearance he was "going in on a semi-regular basis" to help DHS officials address it, he told ABC News.

The breadth of security clearances granted to all sorts of Americans became a topic of national debate on Wednesday, when the White House announced that it had stripped the clearance of former CIA director John Brennan, a frequent critic of President Donald Trump.

"I was in the same position Brennan was in, in the sense that after I left [government] they maintained my clearance for a year in the event that they needed me to come back and provide any type of contextual or experiential information," said Cohen, who is now a paid ABC News contributor and still maintains a clearance so, when called upon, he can support government security efforts.

In all, nearly 4 million U.S. government employees have been granted access to classified information, according to the most recent statistics compiled by the Director of National Intelligence. And that number represents just a portion of all of the Americans who hold security clearances, including local and state law enforcement officials and private-sector contractors, and former officials -- like Brennan and Cohen.

The Trump administration itself has recently touted its efforts to give security clearance to state-level officials, especially as foreign adversaries increasingly threaten U.S. election systems.

In March, Homeland Security Secretary Kirstjen Nielsen told a Senate panel that granting clearances to scores of state officials is a matter "of extreme urgency to the department" so DHS can "share classified information on specific threats."

Similarly, a DHS document published in April noted the value of granting security clearances to those who own and operative private companies tied to the nation's critical infrastructure, including power companies, chemical plants, water utility firms and phone companies.

"With clearances, these owners, operators, and representatives can access classified information to make more informed decisions," the DHS document said.

The U.S. government also grants security clearance to private-sector security operatives protecting U.S. interests overseas, to senior bank officials looking to protect Americans’ savings accounts from foreign hackers, and to high-level officials at hotel chains who spend every day trying to protect Americans staying in their properties around the world.

Cohen, however, noted that the majority of people with clearances are not granted "top secret" access, and that is "a very big difference" because those with "top secret" clearance must pass an "in-depth and thorough background check" and a polygraph exam.

All security clearances are granted after review from "appropriately trained" personnel, according to the State Department.

"It must be determined that the individual's personal and professional history indicates loyalty to the United States, strength of character, trustworthiness, honesty, reliability, discretion, and sound judgment, as well as freedom from conflicting allegiances and potential for coercion, and a willingness and ability to abide by regulations governing the use, handling, and protection of classified information," according to a State Department website covering security clearances.

Nevertheless, even if it's meant to promote national security, the wide array of people granted security clearances doesn't come without its risks. After all, more people with access to secrets means more opportunities for those secrets to be spilled.

In 2013, National Security Agency contractor Edward Snowden shook the U.S. intelligence community when he disclosed a series of highly-sensitive government programs.

That same year, government contractor Aaron Alexis killed 12 people after opening fire inside Washington's Navy Yard. He had been cleared to access the building.

After those incidents, according to a report from Politico at the time, then-Director of National Intelligence James Clapper issued a directive to intelligence agencies expressing his "concern about threats to national security resulting from the increasing number of people with eligibility for access to classified national security information."

On Wednesday, the White House said it was now contemplating whether it would strip Clapper of his security clearance. Like Brennan, Clapper has spoken out against Trump since leaving government.