"In 1972, there was a picture of Richard Nixon and Mao Zedong, who was president of China, and the two of them by shaking that hand, it gave the signal to all the Chinese people that things have changed -- we now have a good relationship with America -- they're now our friends and we're now going to have peace and prosperity," she said.
"I think the pictures of Kim shaking Trump's hand... they're sending that signal to the North Koreans."
The former Trump deputy national security adviser added Kim is also "invested" in his relationship with Trump.
"What Trump's done is he's gotten leverage," she said.
"When you talked about the pictures and some of the people who have criticized Trump and say he's giving him status. He's respecting him on the world stage. That's exactly right.
"Kim is now seeing life in Singapore, he's now seeing life in Vietnam, he's now seeing what the future might hold for him -- not just for Kim, but his leadership."
At the same time, Trump has little to lose by engaging with Kim.
"If nothing happens, Trump walks away," she said. "He calls him Rocketman again."
"If Kim doesn't deliver on this, I think he may have potential problems within his own leadership cadre."
McFarland said former President Barack Obama's strategy did not accomplish any progress with North Korea, and criticized former Vice President Joe Biden for attacking Trump on the issue.
In a tweet, Biden reacted to Trump's visit to the Demilitarized Zone.
"Not one missile or nuclear weapon has been destroyed, not one inspector is on the ground," he wrote.
"If anything, the situation has gotten worse. North Korea has continued to churn out fissile material and is no longer an isolated pariah on the world stage."
McFarland said the former Delaware senator should look to his former boss' actions on the matter before critiquing the current president.
"That's coming from a vice president whose president had a strategic doctrine with North Korea which was strategic patience -- in other words to not do anything."