Is putin meddling down there too?
i doubt it. or they might be, but they don't need to be. amlo has had a base of support for decades, and with the other parties essentially discrediting each other over the last couple of presidential cycles the general view, or at least a majority view is that there's no other viable option. there's also a shift towards him because he's represented an anti-american, nafta-sceptical view for decades and for obvious reasons, that appeals to voters right not.
also voters are weird. my wife just decided she's going to vote for amlo because he's going to win anyways. she's been talking about how bad he is for years.