Liberal activists plan to begin airing a television ad against Hillary Rodham Clinton in Iowa this week, the first non-Republican negative ad aimed at a Democratic presidential candidate.

The group, Democratic Courage, has accused Clinton of making policy decisions on the basis of polls, not convictions. It planned to introduce the ad Tuesday.

Glenn Hurowitz, the group's president, described the spot as a modest buy that would run on cable only, meaning it won't be seen as much as ads by Clinton and rival Barack Obama, who are spending hundreds of thousands of dollars on ads in the state.

Democratic Courage is a political action committee, financed by contributions of no more than $5,000 per person.

"We are concerned that she wouldn't be the best candidate in the general election or the best president because she is so easily bullied by the Republican attack machine," Hurowitz said.

Republican presidential candidates Mitt Romney, Rudy Giuliani and John McCain have all run ads putting Clinton in a negative light.

Hurowitz said the group does not plan to endorse any candidate, though he said it may run a negative ad against another Democrat in the field. He would not identify who that would be. He said the extent of the group's advertising would depend on the amount of donations its first ad generates.

Clinton is in a virtual three-way tie in Iowa with Obama and John Edwards. The Iowa caucuses are only one month away.