A slump in travel demand due to President Donald Trump's trade war has left all U.S. airlines reeling, but the pain is most acute at budget carriers. Southwest, Frontier and JetBlue all saw sharp declines in their operating margins in the first quarter. In comparison, margins at Delta and United Airlines held up, despite faltering consumer demand. As the odds of slower economic growth and higher inflation rise, the margin gap between budget and full-service airlines is expected to widen further.