firm. And the administration might very well be handcuffing itself to a strategy of more warfare as it keeps offering grave warnings about what a victory by the Taliban would mean. These warnings will make it difficult in the long run for the administration to contain the operation or to withdraw forces unless it is absolutely clear that the Taliban has been defeated. Democrats could find themselves feeling like their predecessors in the 1950s who were under political pressure to abide by the containment arguments outlined by President Harry Truman with the Truman Doctrine in 1947 -- first with Korea in 1950 and then with Vietnam. Obama should not be so defensive about the comparisons with Vietnam. Rather, he should use Johnson's experience to help guide him as he makes crucial decisions in the months ahead and attempts to navigate the challenges of the wartime presidency. In a conversation with a few of his closest advisers, Johnson said in 1964 that It's damned easy to get in a war but it's gon na be awfully hard to ever extricate yourself if you get in. In 1965, Johnson made the mistake of excluding those who were trying to warn him about the dangers of the war. Let's hope that this time around Obama does not repeat this error. The opinions expressed in this commentary are solely those of Julian Zelizer.