With its influx of millennials attracted by cheap rents, its punk music scene, and its long-time smattering of anarchist collectives along Baltimore Avenue in West Philadelphia, Philadelphia was a natural incubator for the movement. Four years ago, well before the ascendancy of Donald Trump, the city’s local antifa chapter was one of the first to align with a national parent group. Two years ago, the local chapter hosted the second national annual convention of antifa groups at the Rotunda, an auditorium at 40th and Walnut Streets.