He doesn't have to fulfill a blatantly idiotic campaign promise without losing any points on his popularity.
Mind you, I could be wildly misinterpreting, and I don't have... Like, any facts to support this. Just supposition. But shit man, if this is what he is doing, he's one crafty old fucker.
He's not a crafty old fucker, he's a barely competent con man (vis a vis scamming methodology specifically; most
other things he's by all appearances and history pretty shit at) that happened to luck into a demographic that seriously wanted to be conned and was entangled with a lot of folks that were willing to push it along so they can take various sorts of advantages of the mess, and had been working to prime the demographic in question for someone like him for literal decades. Making impossible or unlikely promises and then blaming something else (particularly while saying you need more funding/support/whatever to overcome said something) when they fall through is confidence scam 101.* It's the basics of basics of how to con someone that wants to believe you.
*I've been around and listening to a scammer trying to defraud one of my grandparents for, like... a half decade now, probably more. "Oh, I tried, but taxes/bank/government/etc./fucking etc. is delaying what I was trying to send! We need a small down payment to clear this up/process the paperwork/etc./fucking etc." There's nothing crafty about this stuff, you just need someone that
isn't going to call you on your bullshit. The tricky part is that latter bit, and trump himself had little to nothing to do with it.
E: Just... just, seriously. Don't play this shit up,
please. What trump did was not some kind of coup, it was the same crap you see out of jackasses sitting in bumfuck nowhere behind a caller ID spoofer, spending their days ripping off the elderly. Anyone willing to throw out any resemblance of ethical fiber can do the same thing, the only unusual bit in this case was the circumstances, not the actor involved.