On further reflection, why don't you make just two word substitutions in the first sentence I reference below to read:
"...their work shows that the top contributors in the United States have earned a bigger and bigger share of overall income..."
Changing just one word in the second sentence that I reference has an even bigger impact to read:
"But both also express bewilderment over the current conversation about whether the wealthy, who have contributed most of America's income gains over the last 30 years, should be paying higher taxes."
Yes, bewilderment indeed! Americans increasingly benefit from the disproportionate contributions of the few.