If you have a law and a politician seems to be breaking it, then the usual answer is to have a prosecutor to look into it.

Politician also have what is called a position of trust, so in addition to legal enforcement there could also be a vote at that political level to remove said politician.

In addition, I would imagine that encouraging people to drink water poisoned with lead can put that politician in legal liability if anyone got sick.

I will add that the US has a odd legal system which potentially give the president permission to ignore laws. The best way to fix that is to remove that exclusive protection, and if its a constitutional problem, fix the constitution.