This is fairly easily disproved by looking at non-US subreddits. I frequent /r/france, /r/unitedkingdom and /r/sweden and non-liberal viewpoints, although less popular, are certainly not silenced. They're just that: less popular (thus more downvotes).
Things are different for the trump subreddit because it's a subreddit that has actively engaged in hostility against other subreddits and particular reddit users. Calls for brigading, slurs and harrassment of other users and admins, I've seen it all by now. It's reprehensible.
The main Trump subreddit would have long been banned and nuked out of existence if it weren't as popular as it is today. Right now, Reddit would face too much backlash if it outright banned the subreddit for continuing not to comply with the site rules. So it's understandable that the admins are trying to handle the situation somehow -- that's not "an effort to reduce [its] visibility", it's a compromise that doesn't involve removing the sub outright.
There's plenty of pro-trump subreddits which aren't involved in this nonsense because they're not spamming, harrassing, using bots etc. You don't hear about them because they get lost in the noise.