As the Biden administration starts work in January, it will face a new raft of national security challenges. Counterterrorism, as with the previous three administrations, will once again be a central concern. The administration will be forced to grapple with old threats, including from the Islamic State and al-Qa`ida, as well as a rapidly changing—and deteriorating—domestic terrorism landscape. Despite 20 years of the so-called war on terror, the battle for the safety of the American homeland remains fraught with challenges and risks. Managing this war will require enduring vigilance and energy, as well as a new set of counterterrorism policies, to more effectively address the totality of the new terrorism threat.