A Wall Street Journal/NBC News poll indicates 20 percent of the nearly 1,000 respondents said they had a very negative opinion of Clinton, compared to 15 percent for Obama and 12 percent for presumptive Republican presidential nominee Sen. John McCain, R-Ariz.

A Pew Research survey indicated 29 percent of Democratic voters asked describe Clinton as "phony," compared with 14 percent for Obama.

Clinton's trustworthiness came under question last week when she admitted to overstating the danger she had faced on a 1996 trip to Bosnia as first lady. The incident prompted claims she exaggerated her role on other issues, such as the Northern Ireland peace process, North American Free Trade Agreement opposition and bringing about child healthcare.

The Clinton campaign has tried to shift focus away from recent debates about her record and toward the economy, an issue polls indicate voters believe she understands better than Obama.