The ethics committee is to decide on or before July 9 whether to conduct a full investigation. But American Crossroads, a group formed by prominent Republican strategist Karl Rove, is already airing TV ads in the state accusing Berkley of "using her office to enrich her family." Berkley calls the ads "relentless smears."
The race's outcome could depend on how Republican Mitt Romney and President Barack Obama perform in Nevada. Obama won the state in 2008, but Republican George W. Bush carried the state in 2004. Five months from the election, Nevada is now viewed as a toss-up in the presidential race.
Before he went to Washington, Heller was a popular secretary of state known for his moderate views. He nearly lost his first House bid in 2006 against tea-party favorite Sharron Angle, who portrayed him as weak on conservative issues.
Since his appointment to the Senate, he's held frequent campaign appearances across the Las Vegas Valley, where the majority of citizens live. Some of his outreach efforts have foundered. Last year he canceled a meeting with the Latin Chamber of Commerce at the last minute, then alienated Nevada' large Latino constituency by saying he didn't support the DREAM Act to provide a route to citizenship for illegal immigrants who arrived in the U.S. as children.
Heller recently announced a group of Hispanic Republican supporters and has been working to restore his image within the community. He's also targeted veterans and business groups.
"No doubt I have work to do in southern Nevada," Heller said.
Berkley said she isn't shying away from Obama or Reid's help. She called Obama's campaign "an asset" and suggested she wasn't worried about turning off voters by teaming up with Reid. "This is a race between me and Dean, and Dean may try to pretend it's a race between him and somebody else. It's not," she said.
Berkley is better known than Heller in the Las Vegas Valley. Voters praise her constituency outreach efforts. "Shelley is always there for the people," said Carolen Tabor, 70, a Las Vegas retiree. "I can see her at Costco and she will hug me."
Robin Joyce, a Republican pastor in Las Vegas, said he is leaning toward Heller. Still, he praised Berkley for her work in the community, support for Israel and efforts to help small businesses.
"She is just a good lady," Joyce said. "She has always stood for Nevada issues."