"Two Days in October" recalls two 1967 events -- a Vietcong ambush and a violent antiwar demonstration at the University of Wisconsin -- that together marked a turning point in America's Vietnam tragedy. The ambush, on Oct. 17, killed 64 of the 142 U.S. troops attacked, and showed, maybe for the first time, that the war might not be winnable. And the protest, a day later against Dow Chemical Co., is believed to be the first antiwar demonstration to turn violent.