I think most campaign donations are made in earnest, by people who support issues. While corruption surely exists, I think most of the time the money is to support the candidate, and help them be re-elected, without any expectation of persuading the politician.
If you look at the donations, this makes tons of sense – big companies, in particular, donate to people who already agree with them! For unpopular causes, even higher donation amounts make sense – you have an ally, and if they get voted out, their replacement probably won't feel the same way. So it's not an issue of Party-X vs. Party-Y, partisan support of an issue. It's a personal delight – the company sees a specific voice they want heard. And, surely, some small percentage of the time it's corruption.
This is probably also why corporations will donate to candidates from both parties. Because their vision is non-partisan! And honestly, most things companies care about aren't partisan wedge issues, so they want to help people in primaries, too.
It shouldn't be shocking for me to imagine people with money and staff using the rule of thumb "they are acting like I would behave if I had money and staff time to vet candidates". And yet, in 2018, the conversation about campaign donations is pretty dysfunctional, so here we are.
I only bring all this up because I see, more and more casually, news organizations and normal people use "has received money from X" as a shorthand for pointing out the corruption of someone they don't like. This is extremely rude! And kind of lazy – you can't possibly know if what you're implying is true, and no effort is made past the implication.
Now, if I said someone was casually implying deeply unethical and possibly illegal conduct, and we were pretty sure they would be wrong the vast majority of the time, I think it's fair to say there is a breach of etiquette. I'm not saying we need to withhold judgment in criminal matters – I'm saying they're innocent, for the most part. And even if they weren't, innuendo is a pretty rude way to engage with the topic.
Some people might say, it isn't corruption, I'm concerned about a conflict of interest – but that's what the corruption is! That is precisely the immoral behavior at issue! It isn't just about explicit quid-pro-quo – I don't want us to lower our standards. I just want us to be more honest, and nicer to each other.