The Gallup Organization said the last time it polled on Roberts, in September 2005, 67 percent of Republicans had a favorable opinion of him and only 4 percent an unfavorable one. In the new poll, taken after Roberts cast the deciding vote upholding the individual mandate in the Affordable Care Act, 44 percent of Republicans said they have an unfavorable view of the chief justice.
"It is a reasonable assumption, however, that a good deal of the shift in attitudes occurred as a result of the June 28 Supreme Court decision upholding the constitutionality of the Patient Protection and Affordable Care Act of 2010, a ruling whose majority opinion was written by Roberts," Gallup said.
Overall, 39 percent of those surveyed said they had a favorable view of Roberts, down from 50 percent in 2005. His favorability rating dropped among independents, from 47 percent to 38 percent.
Roberts' standing has improved among Democrats, with 54 percent now holding a favorable view, up from 35 percent in 2005. Only 19 percent now hold an unfavorable view, down from 31 percent in 2005.
Gallup interviewed 1,014 adults by telephone between July 9 and July 12. The margin of error is 4 percentage points.