Question: Is this a strawman

To the extent that "Tell that to Israel" was an attempt to change the topic to something that the other party thought he could argue better (though I'm betting he couldn't), it was a strawman. However, it was not really irrelevant.

Most of the "wall" along Israel's land borders-- about 97% of it-- is two chain-link fences with a patrol road between them, augmented by electronic surveillance equipment and sensors. There are some concrete walls in populated areas; they are specifically designed to block sniper fire from elevated positions, and are only as long and tall as needed for that purpose.

The "wall" around Israel was made relevant to our own southern border when Thump himself-- not knowing what he was talking about-- mentioned Israel's wall as a good example of border security and something we should emulate.

The person who said, "Tell it to Israel" apparently doesn't know what he's talking about, either, as Israel has found their chain-link border fences to be very effective. On the other hand, the wall that Thump wants to build would, indeed, be ineffective, expensive and an environmental and legal disaster.

As for the weak analogy fallacy, that is Thump's doing, but in his defense, I will note that he pulled it out of his bottomless chasm of ignorance. Unfortunately, a lot of people are happy to walk on the edge of that chasm.