Comparisons between 9/11 and the October 7th Hamas attacks on Israel have repeatedly been drawn. As the Israel-Hamas war enters its fourth week, President Biden has warned Israel not to repeat the US's post-9/11 mistakes. So what were those mistakes, and what, if anything, been learnt from them? Spencer Ackerman is a Pulitzer Prize-winning national security reporter and author of Reign of Terror: How The 9/11 Era Destabilized America and Produced Trump. He writes a newsletter Forever Wars and for The Nation.