What's worse than bombing in front of the president? Bombing in front of the president with hacky material you've already used. Politico caught Leno recycling material from his monologues in his White House Correspondents' Dinner speech, and edited them together.
Leno's White House Correspondents' Dinner speech is already legendary, in the bad way, for not being very funny at all. President Obama's speech—aided by a crack writing team—was relatively hilarious, for jokes told by a sitting president (except for that one about how he would murder teenage virgins with the tools of his unchecked executive power). Now it turns out that Leno's speech was both unfunny and unoriginal.
Politico, which is exactly the kind of news organization that would employ dedicated Tonight Show fans, has assembled a collection of the duplicate jokes.
This is not all that big a deal—comedians and politicians both recycle jokes all the time, so it stands to reason that a comedian performing for politicians would feel right at home doing so. Mostly, it is just sad, that Jay chose those jokes—those awful jokes—to repeat.