Massachusetts Sen. Elizabeth Warren is claiming that the proposed marriage of BB&T and SunTrust vindicates her warnings that bank deregulation will create more too-big-to-fail banks. In reality the merger provides more evidence of how Dodd-Frank’s too-big-to-fail architecture, which Sen. Warren favors, has driven big banks to get bigger and why we need high capital firewalls.

Winston-Salem-based BB&T’s $28.2 billion purchase of Atlanta-based SunTrust would mark the biggest bank merger since the 2008 panic and create...