The U.S. Chamber of Commerce has spent about $1 million to convince people not to vote for Congresswoman Mazie Hirono.
But analysts say the Chamber would have spent even more if it thought Linda Lingle had a better chance of winning.
The latest ads by the Chamber started airing this week. The ads, which cost about $250,000, accused Democrat Hirono of being unable to attract bi-partisan support when it comes to passing legislation.
But while the Chamber's ad buys are big by Hawaii standards, they're much less than the $4 million dollars that the Chamber is spending for Senate races in Ohio and Florida.
Political analysts say that Mainland Republicans -- who once thought of the Hawaii Senate race as a shoo-in -- are placing their bets elsewhere.
"They're clearly decided that there are four or five races they have a better chance of winning and that's where their money is going -- not to Hawaii," said John Hart, HPU communications professor.
Meanwhile, Hirono's campaign says the ads are untrue and show that the Chamber will do anything to win control of the Senate.
"The U.S. Chamber of Commerce has now brought to Hawaii the misleading, negative attacks it's resorted to in Senate races across the mainland," said Hirono's campaign manager Betsy Lin.
Most political analysts now believe that Lingle faces an uphill road in winning in President Obama's home state.
To overcome that disadvantage, they say, she'll need to do well in tonight's final Senate debate with Hirono. She also has to continue to outspend Hirono before the general election, which is less than three weeks away.
So far, Lingle has raised nearly $5.3 million while Hirono has received about $3.4 million.
But in the three months ending Sept. 30, Hirono out raised Lingle by about $600,000, which analysts say indicates a shift in momentum in Hirono's favor.