Jay Leno dropped in on Jimmy Fallon's 'Tonight Show' and killed it: 'They can't fire me'

Jay Leno gave Jimmy Fallon a surprise assist during Wednesday's "Tonight Show" monologue and proved he's still got the chops.

The "Tonight Show" is shooting a week of shows in Los Angeles, which gave Leno the opportunity to drop in on his old stomping grounds. In his second year bringing the late-night show to LA, Fallon says he always hoped his predecessor would make an appearance.

"We asked him if he wanted to stop by the show - we always ask him," he recently told the Los Angeles Times. "He's the nicest guy ever, he never wants to steal the attention. He's like, 'You're doing good, buddy, you don't need me.' And I'm like, 'We do. We want you.' Hopefully, he'll be coming out."

Well, Fallon got his wish. The host faked an injury and said, "I need someone to tag in for me." And then Leno made his entrance.

The former host clearly had some time to make up for. He jumped right into the election, skewering presidential candidates Hillary Clinton and Bernie Sanders. He threw caution to the wind, especially, for a joke about Ted Cruz's campaign commercial featuring a soft-porn actress.

"The campaign said they hired the porn star because they thought she could make Ted Cruz easier to swallow," Leno said.

After the audience went crazy, Leno added, "See, I don't care. They can't fire me."

Leno then launched into the subject of global warming and a rapid-fire series of "It's so hot" jokes. This is where Fallon tagged back in and the two took turns.

That wasn't all: Leno also helped fill some time later when Snoop Dogg got stuck in traffic and ran late for his interview. The comic told Fallon about the time he did a gig for a club owned by the mob and they renamed him.

Watch Leno's "Tonight Show" return below: