If the jihadis want it to tip their way, they need to launch a Tet-like offensive which shocks everyone with its scope and boldness. They don't have to win the attack--just attempting it is enough.
They don't have to read their history, they just have to watch the Senate Armed Services hearings yesterday. Linday Graham made the same handwringing observation yesterday while quizzing Rumsfeld. Unfortunately, Graham seemed to indicate that Tet was a military defeat for the US, when really, it was a huge defeat for the Communists. Of course, Walter Cronkite and the rest of the MSM made it a huge propaganda defeat for the US.
Remember, all warfare is psychology. We can win every battle in Iraq, as we did in Viet Nam, and still lose the war at home, which is all that counts.