“Designated Survivor” isn’t just a fantastical TV show for real-life standbys in chief.

Ahead of President Trump’s State of the Union speech Tuesday, former designated survivors have blown the lid off what it’s like waiting in the wings to become the next president in case a disaster wipes out the real one and the rest of his cabinet.

And they say the scenario made famous by the ABC series doesn’t seem so outlandish in the moment.

“One part of it seems totally unrealistic. Then there’s a certain realism that sets in and you have to take it seriously,” former Veterans Affairs Secretary Jim Nicholson, who was the designated survivor for President George W. Bush’s 2006 State of the Union, tells NBC News.

On the show, Keifer Sutherland’s Secretary of Housing and Urban Development is tapped to sit out the annual speech — then suddenly becomes the president when the leader and every other member of the line of succession are killed in a terror attack.

It’s based on a real tradition dating back to the Cold War that sees one president-eligible cabinet member — a natural-born US citizen who is at least 35 years old — spend each State of the Union and inaugurations in a secure location away from the nation’s capital, accompanied by presidential-style security and the nuclear “football,” ABC News reports.

Such a large entourage doesn’t always slip away quietly. Former Energy Secretary Bill Richardson tried to go on a vacation in Oxford, Maryland, when he was selected in 2000 — and the town freaked out when his motorcade drove in.

“The whole town must have thought there was a national emergency or a fire,” Richardson told NBC News. “It caused quite a ruckus.”

Former Agriculture Secretary Dan Glickman waited out his turn as the unlikely successor in 1997 in his daughter’s Manhattan apartment — along with a small army of secret service agents.

But as soon as the president’s speech was over, the guards left and Glickman went out to dinner — only to get stuck in a snowstorm without a ride, he tells NBC.

“Only three hours before, I was potentially the most powerful person in the world,” Glickman told the news network. “Three hours later, I couldn’t even get a cab.”

But that was before 9/11, when the security surrounding the designated survivor became a more serious concern — as has the secrecy.

“[I] can’t go into the details,” former Secretary of Homeland Security Jeh Johnson, the designated survivor for Trump’s inauguration, told ABC.

The Obama-era appointee did reveal that he had to withdraw his resignation until after the event was over.

“I went from being Secretary of Homeland Security with Secret Service protection and the designated survivor, fourth in line to the presidency, to being a private citizen,” he said.

This year’s designated survivor hasn’t been named yet, and won’t be until right before Trump’s 9 p.m. speech.

Transportation Secretary Elaine Chao is out of the running, because she was born in Taiwan, and others may be ruled out because the president is mentioning their department in his speech, NBC reports.