"I think what could happen is that the more it plays out in the Senate, the more you can see support for removal, especially since the Senate's tone in this proceeding is so much more moderate and benign than it was in the House," Mr. Zogby said.

Earlier polls had found that a strong majority of Americans do not think that the Senate trial will change their opinions. But pollsters like Mr. Zogby believe that further exposure to the facts in the case over the next two weeks or more via television could have a stronger impact on public attitudes toward the president and the scandal.

"The average voter either isn't paying attention to this or, if they ate, they are not overwhelmed one way or the other," Mr. Zogby said. "And that does not play out in the president's favor." "The longer this drags on, I don't see it hurting the Republicans, I see it hurting the president," he said.

The pollsters agree that Mr. Clinton will get a big, if brief, bounce in his approval ratings when he gives his State of the Union address Tuesday.

"He could get as much as 10-point jump in the polls but, as always, they will erode in any number of days," Mr. Zogby said.