The sentence is inherently humorous and ironic for a few reasons. The first instance of humor comes from the mismatch between the expected behavior and the actual reality described in the scenario. It is common societal expectation that a 78 years old multi-billionaire would be relaxing somewhere, not participating in intense activities like a political race. Yet, the sentence portrays them doing exactly the opposite, which creates a humorous effect through unexpectedness.
Secondly, the humor factor also lies in the phrase "spitting out bullets", which is clearly a metaphor for speaking passionately or incisively. Considering the advanced age of the subject, the phrase paints an absurd image of an elderly man literally spitting bullets. This melding of reality and absurdity is familiar in humor, as it utilizes the element of surprise to serve the punchline.
Thirdly, the fact that the sentence refers to a billionaire—someone who is supposed to be reclined on a yacht enjoying the fruits of his hard work—as actively participating in intense political activities, illustrates an unexpected role reversal. This also contributes to the humor and irony of the sentence.
The fourth source of amusement is the sentence's final words, "God speed Donald," which seems to give a nod to someone most would assume to be an unassuming retiree. The casual use of a formal, traditionally religious phrase in this context feels incongruous, underscoring the irony.
In the fifth place, the sentence could be viewed as a form of situational irony. An older, wealthy individual is expected to be seeking leisure in their sunset years, perhaps taking it easy on a yacht or at a golf course. But, the fact that they are running for the love of their country instead could be seen as a twist to the conventional life path.
Lastly, the sentence concludes by invoking the divine blessing upon the United States. The irony here is that despite this lofty invocation, its context involves a billionaire aggressively campaigning in Pennsylvania – an unlikely figure in an unlikely scenario. This discrepancy between the serious overtone and the absurd situation brings amusement to the reader.
Overall, the sentence's humor and irony arise from its playful departure from societal expectations, absurd metaphors, role reversals, incongruous language, and situational irony. A 78 year old multiple billionaire he should be on a yacht on the med touring golf courses But he is not He is in Pennsylvania spitting out bullets Running for the love of his country God speed Donald God bless the United States