HMM: ‘Pendulum Factor’ could land Trump in White House.

If you’re having trouble understanding the phenomenal rise of Donald Trump, buck up — you’re not alone. Even political pros are dumbfounded.

They were shocked when the reality-TV star and businessman first grabbed the lead in national GOP polls. Now they’re double shocked as he soars in primary states, grabbing a 24-point lead in New Hampshire and a 15-point lead in South Carolina.

In one survey, Trump more than doubled his favorability ratings among Republicans in a single month, from 20 percent to 52 percent. The Hill newspaper called the turnaround “political magic” and the poll’s director, Patrick Murray of Monmouth University, called it ­“astounding.”

“That defies any rule in presidential politics that I’ve ever seen,” Murray told The Hill.

Other pollsters made similar comments, but a closer look shows an explanation. I call it the Pendulum Factor.

It reflects the fact that the legacy of each president includes the political climate he leaves behind. In plain English, Barack Obama’s most ­important failures as a leader begat Donald Trump’s success.

This sounds a bit like the Insta-Daughter’s Theory Of Presidential Opposites.