The disappearance on 1 August of Santiago Maldonado, a young political activist and supporter of radical Mapuche indigenous campaigners in Patagonia, is escalating into a major test for the government led by President Mauricio Macri. Thousands demonstrated in Buenos Aires and other cities on 1 September demanding that his fate be clarified. There were violent incidents at the end of the march in the capital, when hooded demonstrators fought with police (the latter responded with water cannon and rubber bullets).Twenty-three people were wounded and 31 arrested, in what was one of the most violent clashes seen so far under the current government. The unresolved case could have a major impact on the mid- term elections due on 22 October.