Costco

Good Unite Us says those numbers are based on donations of the organization or senior employees. I don't know what they consider senior employees, but OpenSecrets has a full breakdown of what individuals affiliated with Costco donated and to whom. Democrats get way higher average contributions, so I'm assuming a lot of that is coming from people higher on the org chart who can afford to donate that much to a campaign. A lot of people donated smaller amounts to Trump, though.