The British election results, like any election result, is the result of unique circumstances and multiple factors. It is also, however, a test of a widely articulated political theory that has important implications for American politics. That theory holds that Corbyn's populist left-wing platform is both necessary and sufficient in order to defeat the rising nationalist right. Corbyn's crushing defeat is a decisive refutation.

Many writers, not only on the left, detected parallels between the rise of Corbyn and the movement around Bernie Sanders. The latter is considerably more moderate and pragmatic than the former, and also not laden with the political baggage of Corbyn's widely-derided openness to anti-Semitic allies. And yet many leftists have emphasized the similarities between the two, which are indeed evident. Both built youth-oriented movements led by cadres of radical activists who openly set out to destroy and remake their parties. Both lost in somewhat close fashion, Sanders in 2016 and Corbyn the next year. And fervent supporters of both men treated their narrow defeats as quasi-victories, proof of victory just around the corner.