The allies were in a poor position to take on Hitler in 1938 because they were in denial about the German leader and his military build up. Right now the radical Islamists are acting like Keystone Cops with bombs in Iraq and rattling sabres in Iran with no real strength. If we leave now, then they'll gain in strength (at the cost of thousands more of their own countrymen's lives) and when the suicidal idiots get their hands on the bomb, what's gone on so far will look like a picnic and our grandkids (any that might survive) will think we're idiots for not remaining strong in the face of a relatively weak but extraordinarily dangerous enemy.