premise: From late 1963 to early 1965, Logevall claims, the Johnson administration faced a deliberate choice about whether it should raise or lower the stakes in  Make it an all-out test of will, which it became, or look for an excuse to leave--perhaps with the claim that the regime in the South had become too ill-behaved to be worth further U.S. support or lives.
hypothesis: The administration never even considered making changes.