Based on careful observation of how the DOJ review phase of that merger played out I believe the DOJ fully intended to tank the AS/HA merger, they just needed to go through some bureaucratic motions to make it look like a reasoned decision.

As part of that process they agreed to a specific timeline... both parties had some obligations but DOJ agreed to either oppose it after a 90 day or review or let it go. They fully intended to oppose.

Then there was this debate thing, and the election became ugly with the incumbents looking to lose over economic issues.

I think the administration told DOJ to not oppose, to avoid economy-unfriendly optics in the runup to the election. The passive aggressive manner in which they let the clock run out on the review period kind of supports that suspicion.

I don't know if DOJ would have succeeded in court, but I'm convinced they damn well intended to try, until they got waved off by the big guy.