Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.) fundraised off New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE’s (D) entry into the crowded Democratic presidential field on Thursday, quipping that New York was “Newark’s suburb.”

“You may have heard of Newark’s suburb, New York City,” Booker said in an email to supporters, referencing the New Jersey city where he used to serve as mayor. Booker noted that de Blasio's entry into the race means that two dozen Democrats are now running.

Booker used the fundraising email to invoke the size of the primary field and the limited number of slots on the debate stage, a frequent theme of his fundraising pitches. The New Jersey senator has signaled that he has met the threshold to appear in the debates.

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To qualify for primary debates, candidates must reach 1 percent in at least three national or primary state polls or have at 65,000 unique donors with at least 200 donors in no fewer than 20 states. If more than 20 candidates qualify, reaching both thresholds will serve as a tiebreaker.

"With such a crowded field, the [Democratic National Committee] will have no choice but to get more aggressive in defining who qualifies for the debate stage," Booker wrote in the fundraising pitch. "That means it’s no longer just about guaranteeing a spot for that first debate, but for future debates as well."

De Blasio’s entry has largely been met with mockery from the right since he announced Thursday, with President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE calling the liberal two-term mayor a “JOKE” and the right-leaning New York Post mocking him on its Thursday cover.