After Kennedy’s Endorsement of Trump, the Two Signal a New Alliance

One of the most attention-grabbing days of Robert F. Kennedy Jr.’s independent presidential bid was also its last.

After toiling for months as an electoral afterthought, Mr. Kennedy suspended his long-shot campaign on Friday and endorsed former President Donald J. Trump in a speech in Phoenix carried live by television networks. Then, he traveled across town to speak in front of the largest rally audience since he began his third-party run last year: an audience of 17,000 at a Trump event at an arena in Glendale, Ariz.

As he shook hands with Mr. Trump amid bursts of fireworks, Mr. Kennedy was, briefly, the star of the show, a new attraction for the Trump campaign. But it was unclear what impact, if any, Mr. Kennedy’s endorsement of Mr. Trump would have on the 2024 race.

Framing his third-party bid as an outsider movement and a breath of fresh air for Americans fed up with partisan politics, Mr. Kennedy initially attracted significant support — more than 20 percent in some early polls — and was especially popular with Hispanic voters. Many voters had said they were frustrated with the lack of choice between two unpopular and familiar candidates: Mr. Trump and President Biden.

But Mr. Kennedy had been falling recently in polls, and plummeted further after Vice President Kamala Harris took the mantle of Democratic nominee from Mr. Biden, luring some wayward Democrats back home. Even those supporters who have remained steadfast to Mr. Kennedy are less likely than others to say they will vote in November, and polls have not provided a consistent answer as to whether Mr. Kennedy’s supporters would prefer Ms. Harris or Mr. Trump.

Still, Mr. Trump and his allies on Friday relished the fact that the former president had won the