Robert F. Kennedy Jr. brought in more than $6 million in fundraising since launching his Democratic presidential primary challenge against President Biden on April 19, his campaign announced on Thursday.

Kennedy's campaign touted that the environmental lawyer and high-profile vaccine critic hauled in "an average of $1 million a day" for the final three days of the second quarter of 2023 fundraising, which ended on June 30.

The campaign reported having $3 million in cash on-hand in their coffers at the end of the second quarter.

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Robert F. Kennedy stands alongside bust of his late uncle, President John F. Kennedy

Democratic presidential candidate Robert F. Kennedy Jr. stands alongside a bust of his late uncle, President Kennedy, outside city hall in Nashua, New Hampshire, on June 20, 2023. (Fox News (Paul Steinhauser))

Former Ohio Rep. Dennis Kuncinich, Kennedy's campaign manager, argued that the fundraising is a sign of "the public's support for a courageous, authentic truth-teller. We are hearing again and again that Mr. Kennedy is catching on because the public is fed up with the media smears. People are answering the attacks by opening up their wallets."

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"RFK, Jr. has shown respect for the intelligence of the American people. The more people hear his message, the more he connects," added Kucinich, who unsuccessfully ran in 2004 and 2008 for the Democratic presidential nomination.

Fundraising, along with polling, is a key metric to gauge a candidate's popularity and a campaign's strength. The money raised can be used for travel, ads, and to build voter outreach efforts. 

Kennedy claimed in an interview last month with Fox News Digital in New Hampshire that "the mainstream media has dismissed my candidacy as an irrelevancy."

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The candidate, who is a scion of arguably the nation’s most famous family political dynasty, trails far behind Biden in the latest polls in the race for the Democratic presidential nomination, but stands in the teens in most of the surveys.

President Biden speaks at the Democratic National Committee Winter Meeting, Friday, Feb. 3, 2023, in Philadelphia. (AP Photo/Patrick Semansky)

Biden grabs 64% support among likely Democratic presidential primary voters questioned in the most recent Fox News national poll, with Kennedy at 17% and best-selling author spiritual adviser Marianne Williamson — who is making her second straight White House run — at 10%.

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While he is the commanding front-runner for his party’s nomination, the 80-year-old Biden has faced plenty of concerns from Democrats over his age and physical and mental stamina.

The DNC is fully backing behind Biden, as the president campaigns for a second four-year term in the White House and at its winter meeting in February unanimously passed a resolution committing its "full and complete support" for the re-election of Biden and Vice President Kamala Harris. Additionally, the DNC has said there will be no primary debates between Biden, Kennedy and Williamson.

Marianne Williamson in New Hampshire

Democratic presidential candidate Marianne Williamson is interviewed by Fox News Digital on July 3, 2023 in Manchester, New Hampshire. (Fox News - Paul Steinhauser)

While Williamson, Kennedy and others in the party are criticizing the DNC and Biden, there is political precedent for the move. No incumbent president has participated in a primary debates in modern times. 

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Last presidential election cycle, the Republican National Committee did not schedule any primary debates as then-President Trump faced a couple of long-shot GOP challengers.

The president's re-election campaign and Williamson's campaign have yet to release the April-June second quarter of 2023 fundraising figures. Candidates have until July 15 to file their fundraising reports with the Federal Election Commission.