The poll found 62 percent of Republicans who participated have a favorable opinion of Trump. That figure falls to only 16 percent of Democrats.
By contrast, 68 percent of Republicans and 30 percent of Democrats have favorable opinions of Ben Carson.
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Carly Fiorina is viewed favorably by 47 percent of Republicans and 29 percent of Democrats.
The poll found a growing gender gap, racial polarization and a less-educated base of support pose limits on Trump's popularity.
Trump unveiled a controversial tax plan at the start of the week. It would cut all taxes for individuals making less than $25,000 a year and couples making less than $50,000 a year. The plan also calls for deep tax cuts to the wealthy and to businesses.
A nonpartisan tax research group found more than one-fifth of his plan's benefit would accrue to the top one percent of income earners and the nation's deficit would balloon by $12 trillion.