We humans, as well as rats and many other beings, have pleasure centers that reward us when we act in evolutionarily adaptive ways, such as when we eat or procreate. Wireheading happens when we figure out how to get the reward in our brains without actually doing what evolution wanted us to do in the first place. The most immediate way to wirehead is to hook up electrodes to the right parts of the brain and obtain direct electrical stimulus, as in the pioneering 1954 study on rats by James Olds and Peter Milner; Wikipedia informs us about subsequent studies showing how "rats will perform reinforced behaviors at the exclusion of all other behaviors. Experiments have shown rats to forgo food to the point of starvation in order to work for brain stimulation or intravenous cocaine when both food and stimulation are offered concurrently". Joelle Renstrom has a nice blog post about this.
Parallels to drug addiction among humans are obvious. Another example is the use of contraceptives in connection with sex; science fiction writer Peter Watts has a wonderful poem about this kind of wireheading.
Now for what is going on with the Trump administration. It has of course always (since 1789) been the case that the President of the United States receives pleasurable positive feedback when he does good work. Now, if he is unable to do good work, or if he is simply lazy, he can try to wirehead and get fake positive feedback without actually doing any good work, such as through rallies with enthusiastic followers in Florida or Iowa, or through North Korea-style cabinet meetings, or through typing tweets that generate thousands of likes and retweets.
I am not in general against wireheading (in particular, I am not opposed to the use of contraceptives), as in many cases I think the hedonic utility obtained is a more important value than whatever it is that the wireheading circumvents. But the White House is not the right place for this. What happens in the White House has so far-reaching consequences for the rest of the world that the single-minded quest for the maximization of just one man's hedonic well-being (which, ironically, doesn't even seem particularly successful) with zero regard for others should preferably take place at some other location where the potential for collateral damage is not as large.