Menendez is seeking his third term against wealthy former pharmaceutical CEO Bob Hugin, who has tapped his own wallet for $24 million to finance a TV-ad-heavy campaign in New Jersey, where Democrats have more than 900,000 additional registered voters than Republicans.
Polls show the race has closed from a double-digit lead for Menendez to single digits, and on Tuesday, the Democratic super PAC -Senate Majority PAC- said it was spending $3 million on statewide ads to help Menendez.
"I think it indicates they're taking this challenge seriously," said Montclair State University political science professor Brigid Harrison of Democrats. "If they thought they were in trouble they'd walk away. I think the spending is an indication of the seriousness of the challenge."
A top reason the race is far closer than expected centers on the 2015 corruption indictment against Menendez in which federal prosecutors charged that he accepted lavish gifts from a Florida eye doctor who is his friend in exchange for helping him with a Medicare billing issue. The trial ended in a mistrial in 2017, and prosecutors dropped the charges in 2018.
Hugin, however, has capitalized on the more salacious details in the trial, calling Menendez untrustworthy and highlighted a Senate Ethics Committee admonition letter that took him to task. The ethics panel concluded that Menendez's actions "reflected discredit upon the Senate."
Menendez defends himself by pointing to votes for women's rights and on health care. He also attacks Hugin over his time at Celgene, which settled for $280 million on Hugin's watch in 2017 over allegations it promoted cancer drugs that were not approved by the Food and Drug Administration.
The company didn't admit liability, and Hugin points to the life-saving drugs that the company makes for cancer patients. The race has gotten uglier, with a new Hugin ad raising old unsubstantiated claims that Menendez patronized underage prostitutes as part of his friendship with the co-defendant in the 2017 trial. Menendez on Wednesday called them "lies."
"This deceitful despicable attack ad tells you everything you need to know about Republican Bob Hugin that he's a slime ball," Menendez said. Hugin's spokeswoman responded by calling the senator a "hypocrite and a liar."
The Democratic group's expenditure comes as Democrats face at least eight other close races in their uphill fight to capture Senate control. Democrats and the two independents allied with them are defending 26 seats Nov. 6. That includes 10 Democratic incumbents running in states that President Donald Trump won in 2016.
Republicans are defending just nine seats, mostly in friendly territory. Asked if Democrats were worried about Menendez, Senate Majority PAC spokesman Chris Hayden said the group is "confident he will win" as soon as New Jersey voters understand who Hugin is.
"It means Democrats are worried that Bob Menendez is in trouble," countered Chris Pack, spokesman for the Senate Leadership Fund, the GOP's giant outside political committee for Senate candidates. "If I'm a red state Democrat fighting for my political life, I'd be very very upset with Bob Menendez" for syphoning money from them.
Hugin has so far loaned his campaign $24 million, making him the fourth-biggest self-funder in the New Jersey's history, according to a tally kept by the state's Election Law Enforcement Commission. Overall, Hugin hauled in over $26 million, according to the Federal Election Commission, and has $3.5 million cash on hand. Menendez brought in just over $11 million so far, and has $5.6 million cash on hand as the campaign enters its final weeks before Election Day, Nov. 6.
Associated Press writer Alan Fram in Washington contributed to this article.