 Once Congress passed the budget, Nixon had to withdraw the troops as it would otherwise cause a major constitutional crisis that would as Karnow put it threaten "...the defense establishment's entire financial equilibrium".Karnow wrote that Laird's "...contribution to America's departure from Vietnam has been underestimated".Under the Johnson administration, the issue of American POWs in North Vietnam had been generally ignored out of the fear that signaling concern about their status would make them into hostages that could be used to extract concessions.