America is under attack. In this case, rather than bombs and bullets, undeterred adversaries are using the cyber domain. Every day, they launch thousands of cyberattacks against American individuals, companies, and government agencies—persistently and incrementally chipping away at our security. Bradley Bowman and Annie Fixler write in RealClear Defense that this relentless barrage may seem like an inevitable reality of 21st century life. However, given the stakes for American national security, simply shrugging and accepting the cyber status quo would be a dangerous mistake. The U.S. has established deterrence in other warfighting domains. Washington can—and must—do the same in the cyber domain.