"The Tonight Show" on Monday decided to have a little fun with Donald Trump's personal cell phone number, which Gawker leaked Monday.

"Wait, why are you helping me?" Jimmy-Fallon-as-Trump asks when President Obama dials him up, offering debate advice.

"Because, it'd be hilarious!" Obama replies. "I just want to grab some popcorn, sit back and watch this [bleep] go down."

Debate prep goes ... as expected. It's worth listening to the whole video just to hear Fallon say "Yuuuge!" and the Chris Christie jokes.