There are already two major problems that make this film impossible.
The first should be obvious. In 1993 American Mailer uses the NorAD tracking radar system to send a stealth bomber back to 1943, where Mahler uses it to destroy Washington and win the war. Germany conquers America, and the American industrial/defense industry is erased. There is no NorAd, no stealth bomber, and no teleporter project to send the bomber to the past. The last of these we know absolutely: German Mailer (who actually probably would not have changed his name, and would remain Mahler, but that’s confusing so we’ll stick with the change) is working on a time machine, and has not worked out the bugs. Thus when May 3rd 1993 arrives, no stealth bomber leaves for the past, and so no stealth bomber arrives in the past in 1943. This sets up a fifty-year infinity loop, one history in which America develops the technology that leaves for the past creating the other in which Germany conquers America and the technology never exists, which reinstates the original history in which it is created and sent to the past.
The second problem is a bit more complicated: Longstreet’s 1984 experiment never happened. Herdeg disappeared from the Eldridge, arrived in 1984, returned to release the Eldridge into 1943, returned to 1984, and then in 1993 the plane went back, so that in 1984 Herdeg never arrived. This puts 1943 into complete confusion–did the Eldridge ever return, or is it waiting for Dave to come back and destroy the machine? The problem is that if Dave does not arrive in 1984, he does not return to the ship.
That, in itself, might not be completely fatal to the story. Jimmy could have returned to the ship without visiting the future, and while that would make his life very different, it is already altered completely by the Washington bombing. Dave, though, is still trapped in the vortex–a vortex which now stretches between 1943 and 1993, with the ship returning to its own time and the bomber traveling to the past end. The Dave that emerges in 1993 has to be the twenty-five year old Herdeg who a moment ago was on that ship, who has no memories of Allison or their son Benjamin, of America winning the war, of anything after leaping over the rail of the ship.
We cannot get past 1984, though, without considering Jimmy. His sequential history included leaping from 1943 to 1984 and then returning to 1943, being treated as mentally injured, celebrating V-E day, being visited by Davey at the ranch, and whether nine years later he is still alive or not, once the bomber is sent back it creates a new history. Now as Jimmy enters the vortex, the 1984 end never opens, so he never travels to the future. Once 1984 arrives, there is no Jimmy to travel to the past, and so the Jimmy that comes back on the Eldridge is not the time traveler. Yet he does come back.
That is the issue. If Jimmy is left in the vortex awaiting the future end, then when the Eldridge returns in 1943 he is not there; he must also emerge from the vortex in 1993 with Dave, when the other experiment occurs. In that case, no one traveled from 1984 to 1943, and history has been changed. However, in this case, no one will make that trip in the next history, so we resolve to an N-jump in which Jim and Dave vanished and never returned to 1943, going instead to 1993.
At the same time, they cannot be here. That is, a hole was opened between 1993 and 1943, but not in this version of the universe; if Herdeg leapt from 1943 to 1993, he would be in the universe from which the aircraft vanished. That universe ends the instant the aircraft vanishes, and everyone in it (in the versions of themselves known in that universe) cease ever to have existed, including Jim and Dave. There is no way for these time travelers to arrive in the universe in which the portal never opened.
The movie still has more disasters ahead, and is worth continuing our analysis.