I am surprised that only hillaryclinton.com has public whois data. IMHO, hidding behind a proxy is not a good cue for trust. Three among four are very slow to load on my PC. I think this very good article should also compare the performances of the websites.
Whois data is more used by spammers than anyone else. It's not like the other sites are purposefully trying to hide their contact information—if they want donations, they'll make sure to prominently display a mailing address.
