The terrorist campaign in Iraq can only succeed if the Sunnis back it. The problem is not infiltration from Syria and Iran. Without Sunni support they would be quickly rounded up.
The answer is to bring Kurdish and Shiite trained forces into the Sunni triangle (which is now taking place), provide US fire power(tanks/choppers/etc) and basically give the minority Sunnis population an ultimatum - stop supporting the bad guys and join the government or we'll let the Shiites and Kurds do whatever the hell they want and back them all the way. Being out numbered 4 to 1, with limited military options - car bombs and IEDs - they would not last very long.
As for Weldon, I think he's being snookered by this Ali source into getting us to go into Iran. He has no training in vetting informants, double agents or anyone else for that matter.
A sizeable portion of Sunnis, if not a majority support the TNA and the government building process. They're just slower at coming around; which is understandable considering their former status under Saddam. They're starting to look towards the future; perhaps they now realize that without much oil in central Iraq a national government is all they can hope for.