Will RFK Jr. help Trump by dropping out and endorsing him? Here's what the polls say.

With Robert F. Kennedy Jr.’s announcement on Friday that he’s suspending his troubled independent bid for the presidency and urging his supporters in key swing states to cast their ballots for Donald Trump, many political observers are asking a simple question:

Will Kennedy’s decision help Trump catch up to — or even defeat — his Democratic rival, Vice President Kamala Harris?

In politics, the future is impossible to predict. But the polls have been clear about one thing — support for Kennedy has been falling for a while.

In a Yahoo News/YouGov survey from last October, for example, RFK Jr. got 9% of the vote in a three-way match up with Trump and President Biden. Yet in the most recent Yahoo News/YouGov survey, conducted just before Biden withdrew from the race on July 21, Kennedy was down to 5% — regardless of whether Biden or Vice President Kamala Harris was on the (hypothetical) ballot.

Before Biden’s exit, other polls showed Kennedy’s support slipping by a little less over time — from an average of 11% last March, according to the Silver Bulletin national polling average, to about 8% by the time the president withdrew from the race last month.

Now that Harris is the Democratic nominee, however, the numbers have largely converged; Kennedy currently averages just 4% in a three-way match-up with Harris and Trump. As the vice president has gained ground — she now leads Trump by 2 to 3 points after initially trailing him by 5 or 6 — Kennedy has steadily shed support.

In other words, RFK Jr. is not just leaving the race with fewer supporters than ever before. Some of those supporters — the ones who might have leaned Democratic but were disinclined to vote for Biden — have probably already shifted to Harris, boosting her numbers.

But how many of Kennedy’s remaining voters — who again represent about 4% of the electorate — will now go to Trump?

It’s likely that this final group — Kennedy supporters who have continued to back him even after Harris entered the fray — skews slightly more to the right than the left.

Emphasis on “slightly.”

Kennedy’s father was Democratic icon Robert F. Kennedy, a U.S. attorney general and senator who was shot and killed just as he was closing in on his party’s 1968 presidential nomination. Kennedy’s uncle, John F. Kennedy, was one of the most beloved Democratic presidents of the 20th century. He was assassinated too.

A lifelong Democrat, RFK Jr. spent much of his career as an environmental lawyer fighting large corporate polluters.

But in recent years Kennedy has become known more as an anti-vaccine conspiracy theorist than as a progressive advocate — and he has become more popular among Republicans than Democrats as a result.

Last October, Yahoo News and YouGov tested five false conspiracy theories that Kennedy has promoted — and without mentioning the candidate’s name, all five generated far more agreement among Trump voters than among Biden voters: that COVID-19 vaccines are more harmful than the virus itself (55% vs. 8%); that climate change is being used as a pretext for imposing totalitarian controls on society (68% vs. 7%); that Prozac and other antidepressants have led to a rise in school shootings (35% vs. 12%); that vaccines cause autism (25% vs. 5%); and that chemicals in the water supply could turn children transgender (8% vs. 4%).

So it’s no surprise that when poll respondents are asked how they would vote both with and without Kennedy on the ballot, about 55% of Kennedy’s remaining voters break for Trump, on average, and about 45% break for Harris.

That split means Kennedy's exit probably won’t affect the election in a dramatic way. If Trump were to immediately gain 55% of Kennedy’s remaining voters, explains data journalist Nate Silver, Harris’s average national lead would shrink from 2.5% to 2.1%.

In reality, the effect might be even smaller. Disaffected by definition, Republican-leaning Kennedy voters have had ample opportunity to support Trump in the past; instead of swinging his way, they could back a different third-party candidate, like Libertarian Chase Oliver. Or they could stay home in November.

A quid pro quo deal to award Kennedy a Cabinet position in exchange for his endorsement — something the independent may or may not be angling for — could tip some of Kennedy's voters toward Trump. But it could just as easily turn others off. And it’s unclear whether Kennedy’s running mate, the wealthy Silicon Valley lawyer Nicole Shanahan, will now give Trump the millions of dollars she’s given Kennedy.

Still, small margins in key swing states have decided both of Trump’s previous presidential elections. That could happen again — and if it does, Kennedy’s decision this week could make a (minor) difference.