Among four factors offered in the poll, experience to get things done in Washington was most often named as the most important: 34 percent of primary voters said so. Second most important was being true to core Democratic values, at 22 percent.
Holt and Pallone are Washington veterans and have claimed to be the "true" Democratic progressives in the race. But among voters who labeled experience as the most important factor, Booker won 42 percent support, compared with 15 percent for Pallone, 10 percent for Holt, and 4 percent for Oliver.
Even in Central New Jersey, where Pallone and Holt have their political bases, Booker got 39 percent of the likely primary vote, compared with 19 percent for Pallone and 16 percent for Holt.
"Cory Booker's lead appears to be impregnable. There is very little in the poll that shows a path for the other candidates to overtake him," said Patrick Murray, director of the Monmouth University Polling Institute.
While Booker has often chafed at the "celebrity" label his opponents have tried to slap on him, his overwhelming name recognition is a key factor in his polling and fund-raising lead.
"At the end of the day, New Jersey Democrats would be satisfied with any of these candidates as their nominee for U.S. Senate. They are simply going for the one they feel they know best," Murray said.
The poll also found that only 28 percent of likely Democratic voters were aware that the family of the late Sen. Frank R. Lautenberg had endorsed Pallone. Lautenberg's death in June set in motion the primary and Oct. 16 general election to fill his seat.
Hours after the poll was released, Lautenberg's son, Josh, sent an e-mail to Pallone backers reiterating his support and urging them to vote.
"Simply put, Frank Pallone will only be your next senator if his supporters get to the voting booth in huge numbers," the e-mail said. "The consequence of not getting involved or assuming this race is already over will ensure victory for Cory Booker. Frank Pallone can win this race but only with your help."
Booker's opponents have struggled to gain traction with voters statewide.
Two-thirds to three-quarters of the likely Democratic voters polled don't know enough about Pallone, Holt, or Oliver to form an opinion of them, the survey said.
More than 70 percent of those voters said they knew enough about Booker, and 64 percent had a favorable view of him.
The Booker campaign has not relented. On Tuesday it launched three new Spanish-language ads, one set to air on television and two on radio. In the TV spot, Booker speaks directly to the camera in Spanish.
The Monmouth poll surveyed 403 registered Democrats who are likely to vote in the August Senate primary. It has a margin of error of 4.9 percent.
The Republican primary field consists of Steve Lonegan, a conservative activist and former mayor of Bogota, and Alieta Eck, a Somerset County doctor. Lonegan has had significant leads in every poll of that race.
Contact Jonathan Tamari at firstname.lastname@example.org or follow on Twitter @JonathanTamari. Read his blog "Capitol Inq" at www.inquirer.com/capitolinq.