This issue has a lot of 1) mixing of issues and 2) "value of hindsight" involved.
An overriding, very American, principal is that we don't leave our people on foreign soil and we bring them home. That's why we devote a lot of resources accounting for those MIA from all of the American 20th Century conflicts. (Especially Korea and Vietnam). The criteria for bringing them home isn't their rank; their level of service...or whether they were "pieces of shit" or not (I'm sure there are "pieces of shit" buried at Arlington).
You bring this guy home; let him face Military scrutiny and justice; and let him face the consequences.
That was done. (Including holding him accountable of the risk he put other soldiers in).
Bringing our people home that are still alive leaves us with difficult options. You either 1) send in a rescue Team or 2) you negotiate that release.Negotiations have historically (and not just America, but for a lot of countries) usually come at a high cost, either in money or what we get in return. (Ask the Israeli's about it).
But we've decided it is part of who we as American's, and that it is worth it.
In terms of what the President did, and how he did it being illegal?
Everything he does seems to either be put on the level of either High Treason or being Un-Constitutional...so I really have no idea what is true and what isn't. I would imagine that him filling out a Tournament Bracket is probably unconstitutional in some way.