Robert F. Kennedy Jr. is expected to announce Monday that he is dropping out of the Democratic presidential primary and will run as an independent. The move would come after Kennedy's calls for a debate with President Joe Biden went nowhere and with Biden continuing to hold a 50-point advantage in primary polling.

But while Kennedy's bid for the Democratic nomination was largely inconsequential, he could play a big role as an independent candidate in determining the winner of the general election.

The polling on an independent run by Kennedy is limited, but the data we do have suggests he would start out as one of the strongest third-party or independent candidates this century.

A Reuters/Ipsos poll conducted this past week among likely voters finds former President Donald Trump at 40%, Biden at 38% and Kennedy at 14% in a hypothetical November 2024 matchup. The 2-point difference between Biden and Trump looks a lot like other surveys we've seen and is well within the margin of error.

But from a historical perspective, the 14% for Kennedy is quite unusual. Consider Gary Johnson, the 2016 Libertarian nominee for president. Like this cycle, the two major party nominees in 2016 (Democrat Hillary Clinton and Trump) were unpopular. Johnson, though, appears to never have hit 14% in any poll when matched up against Clinton and Trump.

Indeed, I can't find any instance of an eventual third-party or independent candidate getting to 14% in a national poll since Ross Perot in the 1996 cycle.

Now, the chance of Kennedy garnering 14% of the vote next November is not high. Non-major-party candidates almost always fade down the stretch.

We can see this, again, by using the Johnson example from 2016. The former New Mexico governor polled at 4% or above in every national poll before September 2020 that met CNN's standards for publication. He averaged 8% of the vote in those polls and frequently registered in the double digits.

Johnson ended up getting a mere 3% come Election Day.

And he isn't alone. At one point in the 1992 campaign, independent Perot led both major-party nominees; he ultimately ended up a distant third. Independent John Anderson was often polling in the 20s in national surveys of the 1980 election, before getting less than 7% that November.

We obviously don't know if or how much Kennedy's polling might change between now and the election. Still, even if he ends up with the same level of support as Johnson, it could make a big difference.

Who benefits more?

At the moment, Biden and Trump are close in the national polls. Some surveys have Biden slightly ahead. Others give Trump the edge. The same is true in swing states like Pennsylvania, where Biden and Trump are within the margin of error of each other.

If Kennedy takes disproportionately from either Biden or Trump, it could tip the balance of the election.

The question, therefore, is: Which one of them should fear a Kennedy candidacy more?

The answer is far from clear at this early stage. Although Kennedy has so far been running in the Democratic primary, his favorability ratings are far higher among Republicans. He was just announced as a speaker at an upcoming Conservative Political Action Conference event, after all.

Still, most of Kennedy's admirers on the GOP side also hold a favorable view of Trump, according to a Quinnipiac University poll from last month. It's tough to see Trump-supporting Republicans voting for Kennedy, even if they like him too.

When you drill down to Democrats (and independents who lean their way) and Republicans (and GOP-leaning independents) who don't hold a favorable view of their party's front-runners, Kennedy is about equally liked. His favorability rating among this group of Democrats is 31%, while it's 32% among this group of Republicans.

In the Ipsos poll of a potential general election, Kennedy got 12% from Republicans and 9% from Democrats. This isn't a big difference, but you could see it helping Biden in a very close election.

The Ipsos poll also found that when an unnamed third-party candidate is matched up against Biden and Trump, Biden comes in with 43% to Trump's 42%. That 1-point deficit for Trump (within the margin of error) is worse for him than his 2-point lead (again, within the margin of error) when Kennedy is included instead of a generic third-party candidate. Kennedy's presence on the ballot could therefore benefit Republicans a tad more.

One thing that does seem true from the Ipsos and Quinnipiac data is that among voters who either didn't vote in 2020 or aren't likely to vote this time around, Kennedy has better net favorability ratings and trails the front-runners by a narrower margin.

This means Kennedy could drive up voter turnout but still not affect the election outcome.

The race between Biden and Trump is so close, though, that I'm not sure either side wants to risk a Kennedy candidacy potentially taking votes away from them.

We'll see what happens over the next 13 months.