...When Abbas and his Arab allies have asked President Obama for reassurances that the talks won't end badly, President Obama is reportedly telling them, including in a recent letter: trust me, I'll deliver Bibi.  

Given these conditions, if Abbas agrees to talks -- as I believe he must -- he should in the same breath throw down the gauntlet to Obama, making clear that direct talks will be as much a test of US intentions and resolve as they are of Israel's and the Palestinians'. He should make the case, publicly, that he is trusting the US to live up to its assurances. He should make explicit his expectation that the US will not just sit by, impotently, if Israel engages in behavior that is inimical to serious, productive, good-faith negotiations -- not unless the US wants to be responsible for wasting what may be the last, best opportunity for peace.  

Abbas has good reasons to be worried about direct talks.

There is every reason to believe that Netanyahu is less interested in an agreement and more interested in protracted negotiations that serve his political interests, both domestically and internationally. One need only look at the recently-surfaced video of Netanyahu talking to a group of West Bank settlers in 2001 -- in which Netanyahu brags that he knows how to manipulate the US and that he personally derailed Oslo -- to understand this concern. Moreover, there is the fact that Netanyahu has assembled the most right-wing coalition in Israel's history -- including people like Benny Begin and Eli Yishai, both of whom are dead-set against the kinds of steps Israel would have to take to get a peace agreement...