Much of the thinking is informed by Bloomberg’s experience in the 2018 midterms, when he spent more than $100 million to become the single biggest Democratic donor, winning in 21 of the 24 races where his Independence USA PAC got directly involved.
Canada has had limited donations laws for a decade now. A centre-left government introduced very limited donations from both businesses (a few thousand dollars at most) and invidivudals (a few hundred). In return after each election the parties were given around $1 per vote for financing. The next government (centre-right) partially repealed this law, obviously because business friendly parties are good at getting corporate donations etc. The Trudeau Government (centre-left) restored these laws. In general there is a whole lot less mudslinging, and sensationalist adds via misinformation and full out lies. In fact their budgets for adds is relatively low and there is a lot more focus on debates, political analysis and platforms.
I think the law was extremely successful in tempering the connections between lobbyists and government.
However most of the Scandanavian countries go much further than this. Political donations are extremely limited. In some countries political adds are not permitted at all focusing the campaign on platforms, political analysis and debates. After watching a selection of American political adds (mostly attack adds, other highly idealised feel-good politicians with images of the American countryside and the politician posing) I really ask myself what on Earth does anyone actually learn from these? Their platforms are barely mentioned and in any case most people already know quite well what the two party’s platforms are, that is with only two political parties usually that ever get elected any seats.
A couple of those countries go much further than even this. A political leader (or a cabinet leader whose position is in a conflict of interest) may not take a leadership role on any topic where they have financial interest, worked for more than 5 years in that industry, have family members or close friends in a managerial role in those industries and they are prohibited from working on a company board in any corporation or lobby group for at least 10 years, more years if it is related to legislation that the leader/cabinet minister/notable-participant took part in. This for me, is the ultimate expression of the separation of business interest and state. I cannot imagine that happening in Spain (while quite democratic, it is also chronically corrupt at every level) and perhaps this would never ever in the United States in our lifetimes.