Airline mega-merger story is all about Trump

United Airlines CEO Scott Kirby floated the idea of a merger with American Airlines while meeting with President Trump last month, according to multiple reports.Why it matters: Corporate America has concluded that federal antitrust approval now comes from the top.The big picture: Airline mergers must be approved by both the Justice Department and Transportation Department.Many of DOJ's top antitrust officials and prosecutors have been forced out and/or resigned this year, after balking at proposed settlements in cases like Live Nation and its Ticketmaster subsidiary. The new model for lobbyists has been to go directly to senior DOJ leadership or, if possible, to Trump himself. It's a sea change for how big business is done, including from Trump's first term, and may be contributing to this year's 53% increase in U.S. merger and acquisition activity.Zoom in: United and American already are among America's largest airlines. A merger would give them more than a 34% market share, easily topping current leader Delta (17.8%).Neither United nor American has commented on Kirby's comments to Trump, nor are there indications of active deal talks.Shares of both companies rose significantly on Tuesday.Catch up quick: DOJ under President Biden blocked JetBlue from acquiring Spirit Airlines in 2023, successfully arguing it would lead to higher prices and reduced choice — and their combined market share is only 8%. JetBlue now reportedly is seeking out a new merger partner.Transportation Secretary Sean Duffy last week said that he thinks there's "room" for some airline tie-ups, without getting into specific names.The bottom line: It's unclear how serious United is about buying American, or how Trump reacted to the idea. What is clear, however, is that United knew where to make its pitch.