President Joe Biden will accept endorsements from at least 15 members of the Kennedy political family during a campaign stop in Philadelphia on Thursday as he aims to undermine former President Donald Trump and marginalize the candidacy of Robert F. Kennedy Jr.

Kerry Kennedy, a daughter of former Attorney General Robert F. Kennedy, niece of former President John F. Kennedy and sister of the current presidential contender, will deliver the endorsements of Biden, his campaign announced.

The decision to highlight the Kennedy family endorsement more than six months from Election Day is an indication of how seriously Biden's team is taking the threat of the long shot bid potentially using his last name's lingering Democratic magic to siphon off support from the president.

Both Democrats and Republicans worry that Kennedy's candidacy could spoil their respective presumptive nominee's campaigns. Biden was using the event, which caps a three-day campaign swing in a battleground state critical to his reelection effort, to also sustain the pressure on Trump.

"I can only imagine how Donald Trump's outrageous lies and behavior would have horrified my father, Robert F. Kennedy, who proudly served as Attorney General of the United States, and honored his pledge to uphold the law and protect the country," Kerry Kennedy will say, according to prepared remarks. "Daddy stood for equal justice, human rights and freedom from want and fear. Just as President Biden does today."

The endorsement was hardly a surprise, as the prominent Democratic family has been vocal that they don't see eye to eye politically with Robert Kennedy Jr., who started as a protest primary challenger to Biden in the Democratic party and now is running as an independent. Biden last month hosted more than 30 members of Kennedy's extended family at the White House for St. Patrick's Day, with family members posing with the president in the Rose Garden and Oval Office.

After the formal endorsement, Biden and members of the Kennedy family were set to meet with supporters at a campaign event, and members of the Kennedy clan were planning to make calls to voters and knock on doors on Biden's behalf.

Several notable members of the family were not endorsing, including U.S. Ambassador to Australia Caroline Kennedy and nonprofit leader Maria Shriver, which the Biden campaign said was due to their nonpolitical professional roles.

Robert Kennedy Jr. has spoken publicly in the past about disagreeing with his family on many issues, but maintains it can be done in "friendly" ways. After a Super PAC supporting his campaign produced a TV ad during the Super Bowl that relied heavily on imagery from John F. Kennedy's 1960 presidential run, Robert Kennedy Jr. apologized to his relatives on the X social media platform, saying he was sorry if the spot "caused anyone in my family pain."

The Democratic National Committee has separately hired a communications team to combat the appeal of third-party candidates, Kennedy first among them. The DNC also filed a recent Federal Election Commission complaint against Kennedy's campaign, charging that it coordinated too closely with an affiliated Super PAC to get his name on the presidential ballot in some states.

Kennedy is also viewed warily by the Trump campaign, which is fearful that he could also pull the GOP voters they need to defeat Biden in November. While Trump has released a recent video saying, "If I were a Democrat, I'd vote for RFK Jr. every single time over Biden," he has also sometimes criticized Kennedy, including suggesting that he is more "radical left" than the incumbent president.

The Kennedy family endorsement is a capstone on three days of campaigning in Pennsylvania.

It was an opportunity for Biden to reconnect with his roots, starting on Tuesday in Scranton, where he lived until he was 10 years old. He swung by his childhood home, a three-story colonial that his family rented, and reminisced about attending Mass at St. Paul's.

He seemed reluctant to leave town the next day, stopping for coffee before heading to the airport. "It's good to be back in Scranton," the president said when a customer welcomed him.

Biden's next stop was Pittsburgh, where he called for higher tariffs on steel and aluminum from China to protect U.S. industry from what he called unfair competition.

But even that event involved some nostalgia, as Biden recalled an endorsement from the steelworkers when he was "a 29-year-old kid" from Delaware running for U.S. Senate.

"It changed everything," he said.