Asked whether the federal government should intervene in Detroit, which this month filed for bankruptcy, Holt said the government needed to stand up to Wall Street. Then he attacked Booker.
"It's worth noting: The three of us are here. One is missing. We don't know where Mr. Booker stands on breaking up the big banks . . . on stopping warrantless spying on Americans. We do know where he stands on vouchers. We don't know why."
Pallone jumped in to voice similar displeasure with Booker. "He's very much with Wall Street," Pallone said. "During the presidential campaign, he criticized President Obama for attacking Gov. Romney over Bain Capital."
Booker's absence is "beginning to perturb us," Oliver told reporters after the debate.
'The same number'
In a statement, the Booker campaign said: "The Mayor has agreed to two debates. The same number of debates as in the last Democratic Senate primary in 2008 despite the shorter campaign season."
The other candidates' preoccupation with Booker may reflect his standing in the polls. In the most recent Quinnipiac University poll, released July 9, Booker led his Democratic opponents by 40 percentage points.
Their frustration with Booker aside, Holt and Pallone on Saturday tried to distinguish themselves from each other.
While both champion liberal causes, Holt called himself the true progressive in the race, and Pallone suggested he was a more practical candidate who would seek to work across the aisle with Republicans.
On health care, they agreed that Social Security and Medicare needed to be protected. But while Pallone said Democrats should focus on implementing Obama's health-care overhaul, Holt said they needed to take further steps toward a universal, single-payer system.
"I also am in favor of a single-payer system," Pallone responded. But, citing what he called tea party attempts to stymie Obamacare, he added: "It wasn't going to pass in the Congress."
On immigration reform, Holt said he would support a stronger measure than a bill the Senate passed recently that, among other things, would boost border security and give undocumented immigrants a pathway to citizenship.
The Republican-controlled House has indicated that it will not take up the Senate bill and instead will take a piecemeal approach to reform. Pallone said Republican opposition makes Holt's proposal unrealistic.
Oliver said she would support a pathway to citizenship and noted that she supported a proposal in the Legislature that would offer in-state tuition to some undocumented immigrants.
The debate, held at WPI-TV's Trenton bureau, was sponsored by the League of Women Voters of New Jersey Education Fund, WPVI, WABC-TV, Noticias Univision-41, and the Record, in Bergen County.
It will be broadcast Sunday on WABC at 11 a.m. and 6ABC at 1 p.m.
The next debate in the Democratic primary is scheduled for Aug. 5. The two Republicans in the race, former Bogota Mayor Steve Lonegan and Alieta Eck, a Somerset County doctor, will hold a debate Wednesday, July 31, at 7 p.m. on News 12.
The general election is Oct. 16.
Contact Andrew Seidman at 856-779-3846, firstname.lastname@example.org, or follow on Twitter @AndrewSeidman.