First flight might be delayed by four hours or so. Line at US immigration may take over an hour... If more than that, you miss the second flight.

I might try this, but I would be aware that there still is a slight risk. Also depends upon the conditions for the second ticket. If a no show means you lose it, or not.

(Admittedly I have taken chances. Over the last 20 years or so, I lost three times. Once at LHR even though I had a three hours connection; I had to buy an expensive last minute ticket and I still missed the first day of a two days meeting. Once at FRA; I had to pay quite a bit extra, and more recently at LIS, again an extra charge of about 100 EUR. But in neither of these cases was there a good alternative, and I was aware of the risks and to take them.)