r/The_Donald is "quarantined" by Reddit, which means you get a gateway page if you visit for the first time, asking if you really want to visit it (try an incognito window). In the HTML, you'll see that there's a "noindex" metatag that Reddit is instructing Google not to index it.
Also, np.reddit.com seems to be excluded from all search engines: https://np.reddit.com/robots.txt.
I'm not sure why Bing is ignoring both the robots.txt and the "noindex" metatag.