Democrats and Republicans dominate the US two-party political system, but independent candidates like Robert F Kennedy Jr and other third-party challengers could have a major impact in this year's presidential election.
Reuters spoke to a dozen strategists who are gaming out how a third-party candidate could land in the unusual US electoral college system.
Early scenarios show a third-party candidate is likely to take more votes from US president Joe Biden, a Democrat, than Republican former president Donald Trump. Even narrow margins could make a difference in a handful of battleground states that are decided by a thin sliver of votes and could go Democrat or Republican.
Those states are crucial in amassing the 270 electoral college votes needed for victory.
Narrow margins and RFK Jr
November's most important battleground states are Michigan, Wisconsin, Pennsylvania, Arizona, Georgia, Nevada and North Carolina.
In the 2020 election, Mr Biden won all these states except North Carolina; they were all decided by less than 3 per cent of the vote.
Mr Kennedy is running on a platform of limiting US intervention in foreign conflicts, cheaper housing and reining in corporate power, and has positioned himself as an outsider alternative to Mr Biden and Mr Trump. He has the support of 15 per cent of registered voters, a recent Reuters/Ipsos poll shows.
Even a fraction of that support could be meaningful in the battleground states, which allocate all their electoral votes to the candidate who gets the most individual votes. Strategists are zeroing in on Pennsylvania, which has 19 electoral votes, and where Mr Biden won with just 50 per cent of overall votes in 2020 versus Mr Trump's 48.8 per cent.
If Mr Biden loses Pennsylvania, he'd need a repeat win of Georgia, Arizona, Wisconsin and Michigan to get to 270. If he loses Georgia, too, then Mr Trump wins the White House.
It could be an echo of the 2000 election, when third-party candidate Ralph Nader ran as an alternative to Democrat Al Gore and Republican George W Bush, some strategists say. Mr Nader was polling at about 5 per cent, recalls Seth Masket, a political science professor at the University of Denver.
"In the end, he only pulled about 3 per cent of the vote in Florida. But that proved to be enough," Prof Masket said. Mr Bush and Mr Gore's vote margin in Florida was so narrow that the dispute went to the Supreme Court, which ultimately decided the election for Mr Bush.
Trump's hard floor
Both Mr Biden and Mr Trump have low overall approval ratings - at or below 40 per cent in many polls - but a third party is not expected to damage Mr Trump as much because his voter base is loyal, strategists say.
That means he is unlikely to lose core voters if any third party is presented, although it is harder for him to gain supporters.
"He probably can't get above, let's say 47 per cent of the vote," estimates Matt Bennett, executive vice president for public affairs at Third Way, a centre-left think tank working with Democrats to thwart third-party bids. "But he also isn't going to drop very much."
Lucas Holtz, a political analyst for Third Way, estimates that Mr Trump's hard floor - or minimum share of the vote thanks to his committed supporters - is 35.5 per cent.
Mr Biden, on the other hand, could gain voters but does not enjoy the same loyal base, strategists say, making him the most vulnerable to a third-party effort. "Uncommitted" protest votes in Michigan's primary last month garnered 14 per cent of the state's Democrat voters who are upset over Mr Biden backing Israel's military campaign against Hamas in Gaza, for example.
No one gets 270 votes
Another question is whether a third-party candidate could siphon off enough of the 538 electoral votes at stake to stop Mr Biden or Mr Trump from reaching the 270-vote threshold. It's very unlikely but not impossible, strategists say. Theodore Roosevelt's third-party Progressives got 88 electoral votes in 1912, while George Wallace's pro-segregation party got 46 in 1968. George W Bush won in 2000 by just five electoral college votes.
Strategists are gaming out two potential "contingent election" scenarios in which no one secures 270 electoral votes.
In those scenarios, a third-party candidate would beat Mr Biden to win Wisconsin, with its 10 electoral votes, or Michigan, with its 15 electoral votes, but Mr Trump would still win Arizona, Georgia, North Carolina and Nevada.
That would result in neither candidate reaching 270 votes, at which point the Republican-controlled US House of Representatives would elect a president by allocating one vote to each of the US's 50 states.
A simple majority, 26 state votes, would decide the presidency, a situation that would elect Mr Trump. Currently, Republicans control 26 state delegations, while Democrats control 22.
The Senate, controlled by Democrats, would elect a vice president from the two vice presidential candidates with the most electoral votes. In that unlikely scenario, the US could wind up with a Republican president and Democratic vice president for the first time in history.
A clean third-party victory?
It is hard for political analysts to envisage a third-party candidate amassing 270 electoral votes on their own because outside of the swing states, either Republicans or Democrats control too much of the overall vote.
Ross Perot, a third-party candidate who got 19 per cent of the national popular vote in 1992, still did not win any state or pick up a single electoral college vote.
"There's no one really that popular," political science professor Masket said.
