Senator Hillary Rodham Clinton heads into tonight’s Democratic presidential debate in Las Vegas with an opportunity: to try to erase the unflattering image that her chief rivals, and her own mistakes, have helped create.

Yesterday, in an attempt to neutralize one possible threat at the debate, her campaign announced that Mrs. Clinton would not support driver’s licenses for illegal immigrants as president. It is the latest formulation of her position, which has shifted since it became a tripping point in the last televised debate on Oct. 30.

Her advisers say they hope the matter will now be off the table, but Mrs. Clinton’s top rivals made clear that they would continue to press the argument they have been making in recent weeks, that she is inconsistent and overly political.

“When it takes two weeks and six different positions to answer one question on immigration, it’s easier to understand why the Clinton campaign would rather plant their questions than answer them,” said Bill Burton, a spokesman for Senator Barack Obama of Illinois, a rival in the race for the nomination.