Sen. Bob Menendez is the top Democrat on the ballot in what many are casting as the most pivotal midterm election in a generation.

So when New Jersey Democrats gathered for a pre-election pep rally, who was the marquee attraction just as Menendez is facing a competitive challenge from a well-funded Republican? It was Menendez's Senate colleague Cory Booker, the man in the spotlight following his Spartacus moment and talk of an election –the 2020 presidential contest, not the 2018 Senate race.

"The next 46 days will be the most defining days of our lifetime,'' Booker told the gathering of the New Jersey Democratic State Committee at the Harrah's Resort and Casino in Atlantic City. "They are leading into an election that will not (only) decide what party will control the House and the Senate, but will speak to who we are as a nation."

Booker headlined the two-day event to fire up the rank and file for House candidates and for Menendez this fall, but it was not until the crescendo of his emotional appeal did he finally give a full-throated plea to turn out the vote for Menendez.

"You can't lead the people if you don't love the people!" said Booker, offering up his signature blend of sermonizing and political pragmatism. After the speech, the party members pinned Booker to the stage, eager for selfies with the celebrity. The push teetered on a frenzy.

At a time when Menendez is facing a competitive challenge from Republican Bob Hugin, a former pharmaceutical executive, Booker has dominated the media spotlight.

The confirmation hearings for Supreme Court nominee Brett Kavanaugh earlier this month have given Booker a national stage to burnish his credentials as a progressive firebrand willing to risk his career, if necessary, to halt the ascent of a conservative Donald Trump choice for the court.

At one point, he likened his clash over confidential documents with Republicans on the Senate Judiciary Committee as an "I am Spartacus" moment, a reference to the Thracian gladiator who led a slave revolt against Rome in 74 B.C. It's a role made famous by Kirk Douglas in a 1960 Hollywood extravaganza, but in 2018, it made Booker stand out against other potential Democratic rivals for president in 2020.

More on Booker:Will Cory Booker be punished for releasing Kavanaugh emails?

NJ election 2018:Menendez attacks Hugin for past stances on women, gays

But as Booker jockeys for the spotlight, it raises the question: Is he indirectly harming Menendez by robbing some of the attention in the final six weeks of the crucial midterm elections?

And the attention on Booker also comes at a time when Menendez, who has been bombarded with attack ads financed by Hugin, could stand to use the free media. And polls show tepid enthusiasm for Menendez among the Democratic Party rank and file.

A Quinnipiac University poll released last month found a vast majority of Democrats supporting Menendez (74 percent), but a comparatively low figure for a high-profile party nominee. Hugin, who has never run for public office, has 85 percent support among Republicans.

And the unexpectedly tight race -- Menendez's 17-point lead over Hugin in April now is 8 points -- suddenly has Democratic operatives sweating it out. The easy Democratic win in blue-Jersey suddenly is competitive.

Most Democrats acknowledge the attack ads, which draw heavily from Menendez's federal corruption trial last year, have taken their toll

Although the trial ended with a hung jury, and with the judge throwing out most of the serious charges, Menendez was still "severely admonished" by the Senate Ethics Committee -- a finding that Hugin's team has recast as a "guilty" verdict leveled by Menendez's Senate peers. The Menendez campaign didn't counter with its own ad blitz, apparently saving resources for the final weeks of the race, when most voters begin to tune in.

"It made a difference,'' Ben Dworkin, director of the Institute for Public Policy & Citizenship at Rowan University, said of Hugin's ads. "That is why people want to spend $20 million to $30 million on a campaign. It allows you to define the other person."

Yet, most Democrats expect Booker to help blunt some of the negative attacks. Booker, who has a close relationship with Menendez -- a far cry from former Senators Bob Torricelli and the late Frank Lautenberg, who openly loathed each other -- has already started serving as a stand-in for Menendez in several of the contested districts. He has helped raise money and plans to stump for Menendez in the homestretch.

And many hope that Booker's star power will transfer to the more staid and low-key Menendez. Booker, whose mastery of social media has boosted his national profile, especially among millennial voters, will also be put to work for the Democratic Party-Menendez cause.

"I will go through fire for him," Booker said last week.

Booker speaks effusively about Menendez, calling him the "best partner one could have ever imagined." But he also touts Menendez's reelection with a pragmatic warning: New Jersey (and the nation) cannot afford to send another Republican to the Senate to back President Donald Trump's ruinous agenda.

You may not love Menendez, but a bolstered Republican majority in the Senate could inflict further damage, the argument goes.

Hugin has cast himself as an independent, who will work to build a bipartisan consensus and buck Trump when he supports policies that inflict harm on New Jersey. But Booker has sought to debunk that claim of independence, noting that Hugin was a Trump donor and a Trump delegate to the Republican National Convention in 2016.

"I think people in New Jersey are really sophisticated voters and they know that they do not want in the U.S. Senate a Trump delegate...someone who will prevent us from having a check and balance on the president, somebody who will support the president's policies,'' Booker said last week.

Steve Sandberg, Menendez's campaign spokesman, dismissed suggestions that Democrats are less than enthused about his candidacy, and says the Senator is greeted warmly at parades and events around the state. He added, "at the end of the day, the Senator is going to have a very strong showing of Democrats throughout the state. I think people understand what is at stake in this election."

Many grassroots activists infuriated by Trump have focused most of their attention on about five competitive House races. New Jersey could play a pivotal role in the national Democratic Party's attempt to regain control of the House for the first time in a decade. Yet the Kavanaugh nomination has also put Menendez back on their radar.

"For us, there is nobody to stop the crazy MAGA agenda,'' said Saily Avelenda, a leader of New Jersey 11th For Change, referring to the acronym of Trump's "Make America Great Again" slogan. Her group is backing Democrat Mikie Sherrill in her race against Republican state lawmaker Jay Webber for the 11th Congressional District.

"For us, Bob Menendez is the only choice we have,'' said Avelenda, who said the group has not formally endorsed his campaign.

Booker, whose career has been financed by Wall Street and Silicon Valley money over the years, also made his own pitch to the grassroots last Thursday on behalf of Menendez and House Democrats. It was a crowd-pleasing line tinged with irony. After all, Menendez has spent the last 25 years in Congress, the last 12 in the U.S. Senate.

"I know that the history of this country is not about a bunch of men in Washington leading us forward to freedom,'' Booker told the Democrats on Thursday. "It's about the grassroots understanding the power of the people is greater than the people in power."