While the standing doctrine is one of the most widely theorized and criticized doctrines in U.S. law, its origins remain controversial. One revisionist view argues that New Deal progressive Justices purposely invented the standing doctrine to insulate administrative agencies from judicial review. Yet existing support for this “insulation thesis” is weak. Our Article provides the first systematic empirical evidence of the historical evolution of standing. We synthesize the theory and claims underlying the insulation thesis and compile a new database of every standing issue decided, along with all contested merits votes, by the Supreme Court from 1921-2006. To overcome conventional problems of haphazard case selection, we amass, read, and classify over 1500 cases cited in historical treatments of the doctrine, assembling a database of all standing issues contested. With modern statistical methods and this new dataset—comprised of 47,570 votes for 5497 unique issues and 229 standing issues—we find compelling evidence for one version of the insulation thesis. Before 1940, progressive Justices disproportionately deny standing to plaintiffs in cases that largely involve challenges to administrative agencies. After 1940, the political valence of the standing doctrine reverses: progressives uniformly favor standing. Justices Douglas and Black, in particular, track this evolution (and valence reversal) of the standing doctrine. While the evidence for liberal insulation is strong, the historical period of unanimously decided standing cases prior to the period of insulation does not support liberal invention per se. Our results challenge legal inquiries of what claims are traditionally amenable to judicial resolution and highlight the unintended consequences of judicial innovation.