Bob Woodward says he's never seen so much political strength from a former president as Trump has

Famed journalist Bob Woodward says he's never seen a former president retain as much political strength as Donald Trump.

"What's going on now really is an iron curtain of obedience to Trump," told CNN. "It's not just polite deference, it is obedience. And it really is an iron curtain because it's so strong."

Woodward spoke after Trump's appearance at a rally Saturday night alongside Iowa Sen. Chuck Grassley, a mainstream Republican running for election at age 88.

"These people, like Senator Grassley, can count," Woodward said. "They can look at the polls. They go to their home states, they talk to constituents. And there's tens of millions of people who support Trump."

During the rally, Trump awarded Grassley his customary "complete and total endorsement." 

Grassley later commented that it "wouldn't be too smart" not to accept "the endorsement of a person that's got 91 percent of the Republican voters in Iowa."

A recent Iowa poll shows Trump with  a higher approval rating in the state than he ever did as a sitting president. And despite Grassley's popularity as a senator – 81% of GOP voters in Iowa support him – he is not as popular as the ex-president.

"This is a political strength that we have rarely seen, never seen from a former president ... Let's face it: Trump's popularity, his power in the Republican Party has grown since he left office. It has not shrunk," said Woodward.