He’s referring to:

The liberal comedian then asked Fetterman whether his shift in various policies had anything to do with his recovery from his 2022 stroke, asking if > his near-death experience had given him a “freedom.”

“Absolutely,” Fetterman responded. “There’s a line from the first ‘Batman,’ Joker’s like ‘I’ve been dead once already. It’s very liberating.'”

“It’s freeing in a way. And I just think after beating all of that, I just really [want to] be able to say the things that I have to really believe in and not be > afraid of if there’s any kind of blowback.”

Notably:

Some of the most progressive and left parts of the Democratic Party are standing for the kind of side that have kinds of organizations like Hamas

He basically broadly cast Palestinians as "because Hamas is among them, they earned their situation.

So nominally Democrat, but he’s been called “Republican’s favorite Democrat” and has been espousing some more right wing sentiment this year particularly.