Giannoulias, currently serving as state treasurer, also accused his opponent, Republican U.S. Representative Mark Kirk, of avoiding the real issues.
The most recent pre-election polls suggest that Giannoulias trails Kirk, and Giannoulias has now gone on the attack in an attempt to make up lost ground.
"This image that Congressman Kirk is a moderate is an absolute farce," Giannoulias said Monday.
The Democrat told the City Club of Chicago audience that Illinois' voters will eventually learn that Kirk wants to return to the economic policies of the George W. Bush administration.
"As people get introduced to Congressman Kirk and his policies over the next seven months, they'll find out what he really stands for," said Giannoulias. "Unfortunately, that's nothing at all."
Six weeks ago, head-to-head polls showed Giannoulias leading by as many as seven points, but surveys during the first week of April showed the treasurer trailing the northshore congressman by four to five points, with some Giannoulias supporters apparently moving to a growing undecided column.
Kirk and his surrogates have focused on the financial troubles of the Giannoulias family-owned Broadway Bank, where Alexi Giannoulias was chief loan officer until 2006.
The Kirk campaign continues to question Broadway Bank loans to convicted felons, some of which were made before 2006.
"[Kirk] has campaigned on one thing and one thing only - Broadway Bank," said Giannoulias. "Just about every sentence that Congressman Kirk utters these days is a noun, a verb, and Broadway Bank."
The next 30 days could be critical for the Giannoulias campaign, as Broadway Bank is expected to fail sometime near the end of this month.
In a video today, the Kirk campaign accused Giannoulias of trying to downplay the bank issue and the bank's alleged involvement with organized crime.
"Alexi Giannoulias misled voters to get elected state treasurer and continues to mislead voters to get elected to the U.S. senate," the Kirk campaign said in a statement.
At his post-speech news conference, Giannoulias said that the continued Broadway Bank controversy had not affected his ability to raise money, although he admitted he raised less than Kirk during the first three months of 2010.
"We had our strongest quarter ever, and we're gonna work hard to make sure we have the resources to win this campaign," said Giannoulias.
Giannoulias said his campaign will release its first quarter fundraising results tomorrow. Kirk released his numbers last week, revealing that he raised $2.2 million since the beginning of 2010.