It isn’t hard to figure out what’s driving the so-called Donald Trump phenomenon that just prompted one-quarter of America’s likely Republican voters to say in a poll he’s the one they want to be our commander in chief.

It’s harder to figure out why the Trump phenomenon blindsided the Republican Party’s presidential pack, the working press and the punditocracy. And why we keep being surprised every time this happens.

This political driving force isn’t really about The Donald or his billions. It’s about the way things happen – and often collide – at the campaign trail intersection of populism and pandering.

As we’ve noted here before, it’s no phenomenon, just a fact that was documented way back in 1968, by a young Newsday Washington correspondent covering an independent presidential candidate who seemed to have just regional appeal – Alabama Gov. George Wallace.

In 1963, Wallace famously declared “Segregation now! Segregation tomorrow! Segregation forever!” and tried to block the integration of the University of Alabama. But President John F. Kennedy and Attorney General Robert Kennedy sent federal officials and 100 Alabama National Guard troops who escorted two black students peacefully to school.

Five months later, President Kennedy was assassinated. Five years later, in 1968, the Rev. Martin Luther King Jr. was assassinated in April. And then, Sen. Robert Kennedy was assassinated on the June night he won California’s Democratic presidential primary. In September, Wallace took his anti-big-government crusade up North – and drew big crowds.

Northerners cheered Wallace’s jabs against “pointy-headed intellectuals who can’t even park a bicycle straight,” federal bureaucrats whose briefcases contained “nothing but peanut butter sandwiches!”

Folks whooped every time he told anti-war protesters he had two four-letter words for them: “work” and “soap.”

So Newsday’s correspondent began asking Wallace rally-goers one question: Which candidate did they like before Wallace came north? Many answered: “Bobby Kennedy.” It sounded mind-boggling to 1968 ears.

So the correspondent asked: Why did you shift from a big-government, pro-integration, liberal Vietnam War dove to a small-government, states’-rights, pro-segregation, Vietnam hawk? Folks replied they never thought of it that way.

“Sure, I voted for Bobby” in New Jersey’s springtime primary, said a Newark postman proudly wearing a Wallace button (and proud of his Bobby Kennedy autograph back home). “He had the same thing Wallace has got that none of the other politicians have: guts. Bobby was a good man because he was not afraid. Now Wallace is the only guy who isn’t talking out of both sides of his mouth at the same time, trying to please everyone at once.”

Mrs. Clifford Dupree, an Edison, New Jersey, housewife, saw her shift from Kennedy to Wallace as a consistency, not a contradiction. “They say what they mean and they don’t beat around the bush,” she declared.

Fast-forward to 2015: Those 1968 answers should seem familiar. That’s what today’s voters say they like about Trump, what 1992 and 1996 voters said they liked about billionaire presidential candidate Ross Perot – and what many say about statewide tea party candidates.

People are drawn to candidates who make promises people want to hear. Even when candidates offer no actual plan. If you can’t trust a man who made billions to make good things happen, who can you trust?

Still, you can also trust that Trump will go too far. Hours after his shameful Saturday belittling of Sen. John McCain’s Vietnam heroism, the Washington Post/ABC News poll showing Trump at 24 percent also showed his support was falling.

Millions who watch reality TV believe they are watching reality. The Donald knows reality is like sincerity – if you can fake it, you’ve got it made. So Trump’s believers aren’t bothered by his birther blasphemies and reality distortions. The reality they know is it’s harder than ever for middle-class people to pay their bills, while only the rich are getting richer.

Trump’s believers are our reality. That’s why it was wrong, but understandable, for a fed-up McCain to call Trump’s audiences “crazies.” They are America’s fed-up voters of 2015. They desperately want to be led and are easily misled.

They’re drawn to Trumps, Perots and tea party fulminators for the same reason they might heed the impassioned command of filmdom’s Howard Beale – if that truth-talking anchor in “Network” (played by actor Peter Finch) implored them on today’s reality TV, as he did in that 1976 film classic:

“I want you to get up right now and go to the window. Open it, and stick your head out, and yell: ‘I’m as mad as hell, and I’m not going to take this anymore!’ ”

If you hear those words echoing through America’s swing-voting cul de sac suburbs on election night 2016, you will know America’s fed-up, mad-as-hell voters just chose your next president.