"Winter Soldier" was filmed in February 1971 when over 125 veterans (including John Kerry) spoke of atrocities they had personally witnessed and/or committed. Bear in mind that a central attack leveled against Kerry in the '04 "Swift Boat" TV ad was that he supposedly gave "aid and comfort" to the enemy in Vietnam. How? Apparently, by telling the truth.
Of course, there were a few GOP senators who briefly said the same thing about Abu Ghraib until John McCain insisted on holding hearings about the torture and abuse that occurred there.
Finally, it should come as no surprise that there were clear connections between Bush operatives and the creators of the anti-Kerry "Swift Boat" ad. Both believe that dodging or distorting the truth and keeping Americans in the dark are justified as long as doing so serves their political ends.
If you have a chance to see this movie, do it.