Lots of people here are focused on one guy. But the the article says "widespread". In my experience, much of the corruption is at a local or state level. At the federal level it seems the corruption is mostly related to agencies (GAO reports) and lobbying.
It doesn't seem like they asked about specific levels or branches of government, so presumably the respondents were giving a general impression. And in that case, it's hard to believe that a corrupt President wouldn't strongly influence the response.
A fish rots from the head down
usaid gec ngo all federal all exist to facilitate corruption