I've been an on and off user of 4chan for about a decade and a half now, and over the course of those years I've had a unique experience being able to witness the cultural power of the website grow and the political Impact It has had. A detailed history of the website should be available within a few hours of this post going live on my page titled "Memes, politics and power; how anime tried to destroy the world"
I'll start off by saying that It wasn't the whole of the user base of 4chan who conspired to make trump the president, In fact It was only a few boards, the largest boards, but still only a piece of what characterizes the website and its users. It Is hard to pinpoint exactly when all this started and Its much more likely that what happened is a culmination of many events and pressures that have been building over decades, or even longer.
June 15, 2016: Donald trump officially announces his presidency.
/pol/ has generally been predominantly republican but only in the last few years have the majority of its american users been vocally outspoken against left wing politics. I suspect this is probably because of the foothold of intellectually dishonest individuals who used third wave feminism as a platform to lie, and manipulate themselves to power. I explain this In more detail in the previously mentioned post.
As time progressed and Donald Trump began getting more and more success on his campaign more people from the influential website began rooting for him. Some did It Ironically because they didn't believe trump would ever win, Others did it to frustrate those they disagreed with politically, and still others did It because they honestly wanted him to win. Now I mentioned the hatred for dishonesty the board held but this does not mean its users are honest and honorable, this is the dual nature of /pol/ and really 4chan as a whole. Since the nature of the website frees its users from consequences of their words via anonymity they are free to express their negative sides, as well as attempt to enforce their moral beliefs. This makes /pol/ a unique area for political dialogue as any view is freely expressed and those who express them are not subject to bans, mutes, or even social rejection. Unfortunately this also means that there are plenty of people expressing very racist, homophobic, and otherwise violently nationalistic ideals, all of whom were seemingly pulled into the grips of our presidents plainspoken language and divisive politics.
Since the inception of our country, the leaders have always been incredibly careful, enigmatic, and fast talking. It was considered Important to always say exactly the right thing at exactly the right time. Many presidents to be have lost it all on a single misplaced word or freudian slip. Donald Trump If he Is anything is a mold breaker, and his apparent lack of verbal self control served, primarily, to outrage people and provide meme fodder for /pol/, and /b/. The outrage worked in his favor as well, TV news in america has long since evolved into entertainment and latched on to his incensing dialogue spreading his face and message to everyone, essentially guaranteeing his success, even to their own detriment, in exchange for ratings and dollars.
Meanwhile, on the other side of the board the DNC were leveraging Hillary Clinton into the run for president as early as 2015, even going as far as to undermine more popular candidates, like Bernie Sanders. The results of this scandal, aided by wikileaks was a large loss of trust in the democratic party, and the democratic process as a whole. This also served to help Donald Trump into office.
In the end I don't believe Donald Trump became president because a majority of people wanted him to, I think It was because people didn't want Hillary or wanted to work against the systems they disliked, weather it be in the name of anarchy, anti-sjw, or alt right politics. Unfortunately this has become an intrinsic part of the nature of american politics and hopefully, in the future, our country will use this time as an example of what happens when we lose sight of ourselves.