Trump.
Not only is it common seeing Trump in Slate's twitter feed, it's rare to see anything besides Trump! It is understandable for the President of the United States of America to be a common topic, but if one posts 2-4 posts regarding whatever Trump has messed up today, it just gets out of hand. The reason this is such a common occurrence is because Trump is a highly criticized individual, especially for millennials, Slate's target audience.
Vague Lead-in Titles, why they're so popular:
On Twitter, home of the millennials , Slate is especially bad about using very vague, cliff-hanger-esque titles to capture the attention of their target audience. With an attention span the size of the ratio of not-Trump-related-posts to Trump-related-posts on Slate's twitter feed, millennials need these short, unsatisfying titles in order for them to delve further into what they find. These titles are used in almost all of the tweets, especially one's as mind-numbing as "Why preteen girls around the world are obsessed with slime."