The topic came up because Kimmel recalled that the last time Penn was on the show, he shared the night with then-president Barack Obama.
"I was relieved the current president wasn't backstage," Penn joked. "I know he's busy." He then mimed tweeting furiously from his phone.
When Kimmel asked if he'd have any interesting in having a dialogue with President Trump, Penn quite plainly said no. "I think you get into a conversation with a three-year-old, you're a three-year-old with him," he said. "There's nothing to do."
Penn then talked about his ongoing activism and work in Haiti in the wake of the 2010 earthquake that devastated the nation. He revealed that he tries to get back there every couple of months to work with the 100 permanent staffers he has stationed there.
"It's always going to be complicated, and especially now it's difficult when we tend to look at our borders as the end of our humanity and it's very difficult to get people focused on just people in general," he said.
As proof of the benefits of working in other nations and with other peoples, Penn added, "We've been able to take some of our lessons learned in Haiti and to start working with some organizations on the ground in Savannah and in Houston and so on. It's been a very rewarding thing for me to be part of and a real learning curve, too."
Later, the actor talked about his upcoming Hulu series "The First," chronicling the fictionalized story of man's first mission to Mars. It turns out Penn has a special connection to space travel via the first man to step foot on the moon. Check out that interview below, and the show when it premieres this Friday.