"This administration's Department of Justice has a different posture than past DOJs, which had a more conservative approach to antitrust measures," said Marc Scribner, transportation analyst at the Competitive Enterprise Institute. He noted it blocked AT&T from buying T-Mobile in 2011.
Most airline stocks fell hard on Tuesday. "What we saw today will have a cooling effect on investors' willingness to put money into airline securities," Scribner said.
CEI's Scribner, citing what he called American Airlines' "ancient fleet of fuel-inefficient planes" and deteriorated terminals, said the pairing may be the last house on the block for AMR, which is counting on the merger to propel it past bankruptcy.
"American, if it isn't able to merge with US Air, is likely to wither away," he said.