Donald Trump in Nevada. REUTERS/Carlo Allegri

President-elect Donald Trump will receive the nuclear briefing on Friday morning, hours before he's inaugurated as the 45th president.

Trump will be given the infamous nuclear codes, and he'll be instructed in how to launch nuclear attacks that could level cities and wipe out millions of people in a matter of minutes.

"It's a sobering moment. It defines the ultimate obligation that you might have," Andrew Card, George W. Bush's chief of staff who was with Bush on his inauguration day, told Politico.

The codes do not go directly to the US's missile silos, but are rather used to verify the president's identity when he gives the order to launch. Once a launch is ordered, it can't be vetoed.

While the briefing is a solemn moment for incoming presidents, it's not an extensive review of nuclear-weapons policy. It's much more simple.

"The briefer is very, very military. It’s a military briefing," Card told Politico. "It’s not a briefing of the conscience. It’s by-the-book; it’s rote."

"It’s kind of like how to use your remote control for the TV."

Former presidents have been awed by the responsibilities presented to them in the briefing.

George Stephanopoulos, Bill Clinton's former spokesperson, described seeing Clinton leave the room after the briefing on his Inauguration Day.

Democrat Bill Clinton (L) is sworn in by Supreme Court Chief Justice William H. Rehnquist (R) as the 42nd President of the United States as his wife Hillary (C) looks on during the inaugural ceremony at Capital Hill. Jim Bourg/Reuters

"The man who would soon command the most powerful military force in the world emerged … silent and more somber than I’d ever seen him," Steohanopoulos wrote in his 1999 memoir.

Former nuclear launch officers have warned against electing Trump — who has little foreign policy experience and has never held elected office — to hold the awesome responsibility of being able to unilaterally launch nuclear weapons.

"The pressures the system places on that one person are staggering and require enormous composure, judgment, restraint and diplomatic skill," the officers wrote in October, as part of the anti-Trump #NoRedButton campaign. "Donald Trump does not have these leadership qualities."

"He should not have his finger on the button."

Trump will be inaugurated on Friday at noon.