Trump, beginning around 2011, seized on the issue -- which had been percolating in the fever swamps on the far right since Obama won -- and used it to cast himself as the lone voice among conservatives willing to stand up to Obama (and political correctness).
That the whole thing was, wait for it, a totally false conspiracy theory was beside the point for Trump. It proved useful to him, so he used it.
Given that origin story, we shouldn't be terribly surprised that Trump's willingness to engage in conspiracy theories as a candidate has continued since he entered the White House.
Take Trump's tweets on Saturday alone. They amounted to a conspiracy theorist's dream.
Let's take these one by one.
The first tweet deals with MSNBC parting ways with host Greta van Susteren. Van Susteren, in a series of tweets, offered no evidence that she left because of any pressure from the bosses that she be more anti-Trump.
The second deals with 27 states rejecting or raising doubts about requests for data from voter rolls made by the Presidential Advisory Commission on Election Integrity
. The objections to providing that information have been bipartisan, with secretaries of state and governors expressing worries about states' rights as well as the possibility that the information could be used to make a case they don't believe exists for widespread voter fraud.
And the final tweet deals, I think, with a story dealing with Russia that CNN retracted 8 days before Trump sent his tweets
. (Three people with ties to that story, including its author and editor, resigned in the wake of the retraction.)
In each of these examples, what Trump does is similar: He takes something that's happened and insists (or insinuates) that there's something more to the story. Something people aren't telling you. Something the "elites" are covering up.
He, of course, provides no evidence to back up those claims. That's because there isn't any evidence. What Trump is doing in each of these three tweets is throwing just enough red meat to the conspiracy-minded to keep them coming back for more (and more)(and more).
What Trump is relying on is the self-fulfilling prophecy that drives all good conspiracy theorists. He knows more than "they" will let him say! Anyone who doubts Trump is part of the conspiracy! And so on and so forth.
Now, Trump didn't create conspiracy theories. He is just taking advantage of their rise, a rise fueled by the NSA's massive program of personal data collection exposed by Edward Snowden, Trump backer Alex Jones and a thousand and one Reddit sub-Reddits that bring together like-minded conspiracy theorists to prove that they can't all be wrong.
What Trump has done is mainstream conspiracy theories for his own political purposes. Much more so than any other past presidential candidate or president, Trump is willing to indulge conspiracy theories that fit his political purposes.
He didn't exactly say that Ted Cruz's father was involved with the JFK assassination but there was that photo of Rafael Cruz and Lee Harvey Oswald
Then there was the time President Obama ordered a wiretap of his phones at Trump Tower
. Sure, everyone in the government denies it but....
There's LOTS more examples. (Millions of people voted illegally in the 2016 election! Muslims were celebrating on the rooftops in New Jersey on 9/11! Etc. Etc. Etc.)
The point here is that Trump knows exactly what he's doing. It's not important whether he believes all the conspiracy theories he helps churn up and push into the mainstream. What's important is that by doing so he benefits politically.
The result? Conspiracy theories -- and the people who spout them -- have never been more prevalent.