WASHINGTON — What is middle class?President Donald Trump and Republican leaders are promoting their tax-cutting plan as needed relief for the stressed American middle class and a catalyst for job creation.Democrats say they're the ones looking out for the middle class, by fighting against proposed tax cuts that would benefit big companies and the wealthy but hurt the average American. It's not easy to exactly define this middle class, whose members are championed and courted for their votes by both sides. Lawmakers and experts have differing views on the numbers.The Tax Policy Center sets its "middle quintile" — third slice of five — of household income, including tax-exempt employee benefits like health insurance, at $48,300 to $85,600 a year.