The Presque Isle mishap is interesting; numerous factors which are all weak links; the accident chain only needs one, and not all were necessarily contributing factors, but in totality, it seems like a potential train wreck viewed head on.
Both Captain and F/O had multiple training failures. The captain had failed upgrade attempts, had left the airline twice to elsewhere and returned, and had failed the ATP ride. the F/O, retired military (not pilot) had Part 91 experience, and failures on his initial certification many years prior (Private, etc). Those are not necessarily factors, but it does seem that a lot of these mishaps occur when one or both pilots have a history of checkride or training failures. A potential weak link.
Medical investigation centered on the First Officer, who as pilot flying, had sleep apnea, and who reported not using his CPAP prior, and "getting in late." Fatigue may have been an issue, and certainly a potential weak link.
The flight flew the ILS once, went missed, and shot the approach again, with identical results. On the first approach, the F/O reported seeing himself aligned with a "tower" that he knew "wasn't right" (weather observation tower right of the runway, as it turned out), and though the captain saw it on the second try, the F/O reported being heads down and never saw the tower the second time. The captain called the lights on the second attempt, though the flight wasn't remotely close to being aligned with the runway.
Both pilots filed ASAP reports after the fact, citing localizer misalignment on the date of the mishap, and on a prior flight. Another pilot at Commutair also filed an ASAP report for the same time period, several days prior, reporting the same.
An interview with an ATC specialist notes that while center received a report of a localizer misalignment, they were waiting for a second aircraft to report the problem and wouldn't consider it a problem, or pass it along, until the second report was obtained. Until then, ATC would assume that the problem didn't exist.
A check flight, post-mishap, verified that the localizer was not within tolerance, the marker beam too narrow, and a glideslope reversal occurred on the approach; the approach had to be subsequently maintained and returned to service. A note exists in the report that the issues were corrected following snow removal.
When the Captain called the runway and lights, the First Officer stated that he'd remain on the flight director, because he didn't see anything, and later described the view as a complete white-out.
There are numerous factors associated with the event to which blame may be attached, but in the larger analysis, whether the localizer led the crew astray or not, the crew had a responsibility to ensure the safe operation of the aircraft. In particular, the Captain, as pilot in command, held ultimate responsibility.