HARRISBURG, Pa. (WHTM) — How will Robert F. Kennedy Jr.’s now-highly-likely appearance on November’s presidential ballot in Pennsylvania impact President Joe Biden’s chances of winning re-election and former President Donald Trump’s chances of unseating Biden?

One clue came just hours before the Kennedy campaign’s announcement.

Given just the choices of Biden and Trump, a Emerson College poll for abc27’s parent company Nexstar, released Thursday morning, found 47.3% of likely voters would chose Trump if the election were held now, while 45.2% would choose Biden, a difference of 2.1 points, just within the poll’s 3-point margin of error. The rest were undecided.

Given other choices, 44.8% stuck with Trump, an increase to a 2.6-point margin over Biden’s 42.2%. Another 4.9% said they would vote for Kennedy, and 0.9% said they would vote for Green Party candidate Jill Stein.

Stein runs to the left of Democrats and is widely believed to siphon primarily Democratic votes — this year, that would hurt Biden. Analysts are more divided over Kennedy’s impact. As a starting point, the iconic Democratic surname could siphon votes from Biden. But some of Kennedy’s positions — for example, his skepticism of vaccines — are popular with some Trump voters.

If Stein is taking considerably more votes from Biden than Trump, then the 0.5-point growth in margin for Trump when adding both could imply a nearly even impact by Kennedy on both Biden and Trump.

Third-party candidates generally bristle at being called “spoilers,” saying they have just as much of a right as major-party candidates to be on the ballot, and Kennedy’s campaign is no exception.

Citing a Zogby poll commissioned by the Kennedy campaign showing Kennedy could defeat Trump in a two-way race, “the only spoiler in the race is President Biden,” the Kennedy campaign said in a statement last month.

In modern history, the only third-party candidate generally considered by nearly all analysts to have swung a presidential election was Ralph Nader in 2000. Nader — who ran to the left of Democrat Al Gore — was widely considered to hurt Gore more than George W. Bush, who won Florida and thus the presidency by 537 votes; Nader got 97,488 votes in Florida.

In 1992, third-party candidate Ross Perot got even more votes nationally than Nader in 2000. Many analysts thought Perot hurt then-President George H.W. Bush more than his challenger Bill Clinton. But because Clinton defeated Perot by a wide margin, analysts were split on the question of whether Perot’s candidacy impacted the election’s outcome.

Regarding the 5.8% of Pennsylvania voters who told Emerson pollsters this week they would vote for either Kennedy or Stein, it’s important to keep one thing in mind: Voters regularly overstate their enthusiasm at this point in an election cycle for third-party candidates compared to how they actually vote in November, after some voters conclude their preferred third-party candidates have little chance of winning an election and decide to back their favorite among the two major candidates.

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For example, on June 21, 2016, an average of 11.4% of likely voters were telling pollsters they would vote for either Stein or Libertarian Gary Johnson if the election were held then, according to polling data from Real Clear Politics. That November, just 4.4% of voters actually voted for either Stein or Johnson.

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