This reflects badly on the system, not so much Trump (unless he keeps butting in the whole mess). The whole diplomatic immunity thing has great reason to be despised. But it is not because I guess it keeps countries from abusing laws to entrap foreigners. I don't see an up side for Trump to meddle in it, even as unfair as it seems to the kid and his family (like previous pointed out, they got the short end of the stick).
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Not an argument, simply an observation.
The Natural Law governed Man's behavior many thousands
of years prior to the emergence of structured Religions.
One precept asserted that we alone are responsible for our behavior.
This gal drove on the wrong side of the road, suck the teen, killing him,
then ran away; hiding behind diplomatic immunity!
This is the behavior of a disgraceful coward who would have been
treated w/extreme harshness in earlier times when character mattered.
Such behavior says volumes about what we have become as a people.