You can already do that though the regular old banking system, no difference there. Banks monitor and take action when they detect money laundering systems in their transfers, and they use graph analysis that's not dissimilar from the analysis law enforcement uses for tracking anonymous wallets. The mixers in the cryptocurrency world exist as school kids acting as fencers in the real world. A crime ring could definitely "taint" a politician's bank account if they wish to do so, but the manual oversight of the banking system probably wouldn't flag them.

It's not that this isn't a problem with cryptocurrencies, it's just that it's a problem that already exists in the real world.