It feels like the 1950s in the Labour Party. A week that began with important victories for Jeremy Corbyn in the High Court and National Executive Committee elections has ended with a witch-hunt of sorts.

First in a Guardian interview party deputy leader Tom Watson alleged that “Trots have come back to the party,” continuing that “some old hands [are] twisting young arms in this process.” He followed this up with by sending a dossier to the press, which claimed to reveal the extent of the “infiltration.”

The campaign is not surprising. Like many of the attacks waged on Corbyn by the Labour right this line has been deployed before, more effectively, by the Tories. What gives Watson’s allegations greater weight, however, is not their substance but their implications. In conjuring a Trotskyist conspiracy behind the Corbyn movement, his aim is broader than misrepresenting the politics of hundreds of thousands of Labour supporters. If left unchallenged, Watson’s McCarthyism will pave the way for attacks on party democracy and far greater policing of political opinion.