Meanwhile, Fischer released an internal campaign poll showing her down 4 points on state Attorney General Jon Bruning (R) — within the margin of error.
Bruning took 30 percent to Fischer's 26 percent in the poll by Republican firm The Singularis Group. Stenberg, who has come in second place in most polls of the race, came in third in Fischer's poll with 18 percent.
The poll of 400 likely GOP voters was conducted May 6 and had a margin of error of plus or minus 5 percentage points.
“Polls released by a political campaign a week before the election should be taken with a grain of salt," said Bruning's campaign manager, Trent Fellers. "Jon's support continues to grow from the thousands of volunteer phone calls being made and the numerous endorsements he's received both statewide and across the country."
Others questioned whether Fischer's poll oversampled the Lincoln, Neb. media market — the only market where Fischer has been on the air.
But another poll released Monday — this one by We Ask America — suggested that while Bruning still has a lead of more than 20 points over both of his opponents, Fischer has now eclipsed Stenberg for second place.
"What we do know is Bruning's in trouble," said Stenberg spokesman Dan Parsons. "What we don't know is where these people are going."
Fischer also released a television ad Monday, portraying her as a tough-talking leader with a proven record of conservatism.
A source tracking the ad market in Nebraska said Fischer had reserved $27,000 in airtime for the final week of the campaign. Stenberg has reserved about $13,000, the source said, while Bruning has reserved about $300,000 including television and radio.
A Stenberg aide disputed those figures and said Stenberg would spend more than ten times that statewide in the last week of the primary.
"Nebraska-tested and trusted. Conservative, pro-life, pro-gun, cut taxes and cut spending in the legislature," says the narrator in the ad. "Deb Fischer works the Nebraska way: responsibly."
The winner of the May 15 primary will face former Sen. Bob Kerrey (Neb.), the Democratic recruit, in November. The Hill rates this race as leaning Republican.
Watch the ad:
- This story was posted at 6:07 p.m. and has been updated.