According to the Constitution-
Treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort.
What Private manning did was incredibly destructive, damaged US National Security and quite likely put US troops at greater risk in Iraq and Afghanistan. But it wasn't treason, because Manning had no desire to aid our enemies. In order to believe that Manning is a traitor, you have to believe that he intended to get the information he stole into the hands of Al Qaeda, Iran, Hezbollah, or any other radical Islamic terrorist group. The prosecution found no evidence that Manning had any correspondence with Islamic terrorists, sympathized with their ideology, or in any way wanted Islamic terrorists to directly benefit from his actions.
To put Manning's action in context, consider another American who many hailed as a traitor for giving aid and comfort to the enemy; Senator Harry Reid.
"I believe myself that the secretary of state, secretary of defense and - you have to make your own decisions as to what the president knows - (know) this war is lost and the surge is not accomplishing anything as indicated by the extreme violence in Iraq yesterday," said Reid, D-Nev.
Sen Reid made those comments in April, 2007, just when the Sunni uprising was getting started and the Iraq Surge plan (of which my unit was a part) was ramping up to full strength. Reid's comments were blasted by my fellow soldiers in Iraq as cowardice, traitorous, and likely to get us killed because it gave the enemy hope.
But like Manning, Sen Reid clearly never meant to benefit Al Qaeda with his words. He wanted to hurt the president politically and score points with the chattering class, but I don't think anyone in their right mind would accuse Sen Reid or Private Manning of wanting radical Islamic terrorists to win their war against America.
PFC Bradley Manning is a pathetic, confused young man who took out his frustrations with disappointments in life by stealing classified information and leaking it to a political grandstanding whore. His goal is doing this wasn't to aid the enemy, but to cause chaos so he could laugh at the mess he created. Stupid, criminal, and worthy of a long prison sentence, but not treason.