On the trade-off between limiting contagion and keeping routes in service, Mr. Trump said at a press conference Wednesday: “It is a calculation we’re looking at right now.” We’re looking at it very strongly.” Added Mr. Trump: “We are thinking about hot spots.”

Mr. Trump’s remarks illustrate the dilemma facing the nation’s carriers, as they struggle to deal with plummeting passenger demand and closures of air-traffic facilities, even as the Treasury Department is pressuring airline executives to maintain schedules as a condition of federal financial aid.

With passenger counts down 90% or more at some major U.S. airports, many airline, union and government officials consider further flight reductions inevitable. But Mr. Trump didn’t signal such a decision had been made, and an airline- industry official said Wednesday there had been no notification that any changes were imminent.