The co-author of "The Israel Lobby" is, indeed, pretty unhinged:

The Israelis can do almost anything and get away with it….If I went to the Middle East, and visited Israel, and I was killed, somebody shot me, do you think there would be any accountability? Seriously. If any of you went to the Middle East and were killed, do you think there would be accountability? There wouldn’t be. This is how outrageous this situation is. Just think about the [USS] Liberty, think about Rachel Corrie, think about this Turkish-American who was just killed on the flotilla.
The lobby believes it can finesse any issue. They’ve never seen an issue that they can’t finesse…..America’s interests and Israel’s interests are going to continue to diverge. And the end result of that, back here in the United States, is that the lobby is going to have to work overtime to cover that up and make it look like everything is hunky-dory when in fact it’s not.

When his book came out, a lot of people who wanted to change the nature of the Middle East debate became very invested in arguing that Mearsheimer was a sober thinker who deserved to be treated seriously. He isn't. Now, I don't know how reliable "the Judeosphere" is. If they're inaccurately reporting his comments, or taking them materially out of context, I'll update. But this sort of wild talk is consistent with other public statements by Mearsheimer.