That did little to dissuade Kennedy from crossing state lines Thursday to campaign in New Hampshire for Warren, whom he has known since he was her student at Harvard Law School. Kennedy, the scion of one of America's most prominent political families, lavished praise on Warren and touted their personal history during stops at her campaign offices.
Hanging over the visit, however, were questions about whether Kennedy will challenge Warren's fellow Massachusetts senator, Ed Markey, in the state's Democratic primary. The move could spark an intraparty firestorm in one of the nation's most reliably Democratic states, with Warren at the center.
Kennedy tamped down the inherent awkwardness of the political triangle between him, Warren and Markey during his campaign stops in New Hampshire.
"I cannot imagine that (Warren) has given one iota of thought or stress as to some decision about this race, at all," Kennedy told reporters after a stop in Lebanon. "I think she's got bigger fish to fry than an issue on this. I don't think that's causing her lost sleep."
Although Kennedy has filed campaign paperwork with the Federal Election Commission, he has not officially decided whether he will challenge Markey. On Thursday, the 38-year-old said he was still "working through it."
Warren has already endorsed Markey, and his campaign recently released an ad of the presidential candidate promoting his reelection. Markey has also campaigned for Warren in New Hampshire, which holds the nation's first presidential primary.
Even so, Kennedy may be a bigger draw for Warren than Markey in New Hampshire, a state that will be key to her chances of winning her party's nomination for president.
Kennedy "has a huge fan base in New Hampshire," said Ray Buckley, the Democratic Party chairman of New Hampshire, tying back to his family's work in shaping the state party and his own campaign work in the state.
"If it wasn't for the Kennedy family's involvement, the modern-day Democratic Party in New Hampshire wouldn't exist," Buckley said.
Kennedy didn't mention his Senate ambitions as he talked to small crowds of voters at a pair of Warren campaign offices. He instead focused on his personal history with the presidential candidate, fondly recalling Warren's time teaching him at Harvard.
"There's a long-standing great friendship between Elizabeth Warren and Joe Kennedy that goes much deeper than, I think, the professional relationship she has with Ed Markey," said Mary Anne Marsh, a Democratic strategist in Massachusetts.
Markey, 73, isn't the most obvious candidate for a primary challenge in a party that's recently seen several young progressives topple more seasoned, less liberal incumbents. He's well regarded in Massachusetts and has championed progressive issues, including on climate change.
What Kennedy has that Markey lacks is the same aura of generational change that propelled 37-year-old Pete Buttigieg from a little-known mayor of South Bend, Indiana, to a nationally known presidential candidate.
What Markey has that Kennedy lacks, of course, is Warren's formal endorsement. Warren told reporters last month that Kennedy is "an amazing person," but she made no move to distance herself from Markey.
When Kennedy was asked Thursday if he has spoken with Warren, he said, "I've had a number of conversations with her. I'm going to keep those conversations private and defer to her as to how much of that she wants to reveal."
Back in Massachusetts, support for Warren's presidential bid doesn't ensure those same voters would stick with Markey if Kennedy decides to challenge him.
Bliss Austin Spooner, a 53-year-old Warren supporter from Cambridge, said she's leaning toward supporting Kennedy if he primaries the Democratic incumbent.
"It's either kind of good audacious or bad audacious depending on who you talk to," she said of Kennedy's possible run.
While New Hampshire voters may not have a say in sending Kennedy to the Senate, some who saw him speak weren't enthusiastic about him weighing a run.
"Doesn't it feel smarmy to you?" pondered Barbara Jones, co-chair of the Upper Valley Democrats.
Associated Press writer Elana Schor contributed to this report from Washington.