[qquark]

I think some answer might lie in the question of what the speaker is trying to accomplish by swearing.

If you think about it, why swearing instead of using standard words ? Putting aside "bad" habits (I put this into quotes because I don't think there is something inherently bad in swearing, it's just a subset of vocabulary data being transmitted to convey information ;) ), I would say that that goal is, subconsciously or not, to increase the emotional impact of what is being said. This will to increase the emotional impact can stem from the speaker's own emotional state, that needs to be expressed through speaking. This might be for lack of better words in one's vocabulary, "accessibility", perceived "style", etc.

The person is stating something, that might be originally emotionally weak or neutral, but by swearing, he emphasizes the emotion associated to those words or sentences, and thus has the opportunity to convey an additional specific type of information, in a specific way.

I would even say that swearing might be even difficult to replace in some cases where the intended effect is to be casual, or maybe to sound "cool" to a certain crowd while keeping this emotional effect. This might, in a way, be considered "manipulation" if done consciously.

And I think this logic applies very well to Trump particularly, because appealing to people emotions seems to be mostly what put him in office. Rather than trying to win by giving the population high logic on the reasons why he should be elected, he is going the other way: make them feel things that put him under the spotlight as a good contender for the position of president ...