A combination of upvotes and views and amount of both within a shorter time gets memes to the front.
Trumpites outnumber anti-Trumpers and whatever else, so memes they favor have a greater chance. Mind you, most memes by anyone don't make it that far to begin with.
Interaction with other memers establishes a base that might go looking for the work of certain memers. Thus popular memers have more hits. The top memer on this site can meme a fart and it'll hit #1.
Quite a few Lefties (not all) are rather stingy with upvoting, even with those they high five. That mindset isn't going to help like-minded memes make any headway. Maybe they think they can turn the uv's they saved in for tp.
Time of submission is another factor, as early in the morning is best from what I heard.