I don't know that either Kushner or Trump ever pretended to be frum. They belong to an orthodox congregation, that doesn't mean they are observant. Whatever they do in their private life is their choice. As far as I am concerned and you should too, Ivanka is Jewish because a rabbinic court says so and that is what counts in Judaism. So if she violates shabat it doesn't invalidate her conversion it means you should not differentiate her from any other Jew from birth in this case.
However, it becomes very tricky when:
If (assuming it is true as you say, which I don't know for sure but suppose you were right that) "neither of them ever pretended to be frum" - as in, no real interest in keeping mitzvot and no real effort to do so, that indeed calls into question the conversion and its halachic status. That is what Chaim has been pointing out.
Because the conversion does require a certain commitment and real reason of belief for doing so (not just for marriage or joining a shul). Now what precisely those commitments are or what exactly potentially invalidates a conversion is a matter of huge debate in recent eras, especially the current one. And I am not saying they don't keep halacha at all or anything like that. But based on what you said, if it WAS true, then your conclusion does not follow from that, that she is scott free off the hook. No sir.
But I believe the argument in her favor is more like she does keep certain things and did have sincere belief and/or maybe still does. That makes the waters a lot muddier, and then you could argue like you do.
Topic: Wait… What? Ivanka Trump Gets Pass to Travel by Car on Shabbat for Inauguration (Read 8517 times)