But McBride said there is an evolving expectation that first ladies should be more engaged in "advocating and standing for something."
That has the potential to open them up to more controversy. But both head into the fall well-positioned.
Mrs. Obama was viewed favorably by 70 percent of adults in a May AP-GfK poll, compared with 58 percent for the president. She was viewed unfavorably by 20 percent, her husband by 38 percent.
Mrs. Romney, less well-known, was viewed favorably by 39 percent and unfavorably by 23 percent, while 38 percent did not know how they felt about her. Mitt Romney, better known, had higher unfavorable ratings than his wife. He was favorably viewed by 43 percent, unfavorably by about the same share of voters, with 13 percent unsure about him.
AP Deputy Director of Polling Jennifer Agiesta contributed to this report.
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