A rally is not required, only that the grounds be used for political reasons.
Then the problem is clearly with this interpretation. According to this interpretation if a reporter writes an article saying that a pro-war politician hypocritically visited the military cemetery, then that reporter used the cemetery grounds for political purposes and should be fined/arrested.
How many politicians have pictures of themselves laying a wreath at Arlington National Cemetery? Can we just assume that it is many politicians, or do we need a collage of demonstrative photos? It could be argued that any sharing of a picture or video of a politician at Arlington is used for political reasons, as it would imply a moral or patriotic message about that politician.
Even in your own wording we find a concession that the interpretation is wrong. You are saying that the grounds cannot be used for political reasons. The grounds were used for non-political reasons at the time of the event. The photos of a non-political event were then distributed for political reasons. Talking about or looking at photos or video of an event is not a continuation of an event that is done and over, and nor is it use of the grounds, and can therefore be freely politicized.
Use of the grounds has a specific meaning. For example, if you are talking about a picture of a public park it is not use of the grounds.
You can obviously write an article about politicians visiting the cemetery with your own political slant, and you can also obviously share and talk about photos or videos of politicians visiting the cemetery with your political slant. This right extends to the politicians talking about their own visit as well. Arguing that you can talk about it with your political slant but Trump can't would clearly be a terrible argument.
Trump grinning and flashing a thumbs-up in that picture - beyond being incredibly tacky and inappropriate
In one post you are wishing that Trump had been shot in the head and assassinated, and in another post you are a colonial era puritan who says it is inappropriate to smile or display positive gestures at cemeteries. So we can stop reading your larp with any seriousness right there.