Hot Air had this item today about CNN political analyst David Gergen's assessment that Barack Obama's visit to Iraq crossed the line from "fact-finding" to outright unauthorized negotiations.
I'm somewhat surprised that neither Ed Morrissey nor any of the commenters (besides myself, long after the thread was dead) mentioned the Logan Act, which expressly forbids negotiations with a foreign government by unauthorized persons.
Ed says it really doesn't matter because "Both Republicans and Democrats have gone on “fact-finding missions” to Iraq in order to bolster their own policies". Bolstering their own policies, yes. Negotiating troop levels? No.