Jody Hendryx, Gaia Lamb and Dale Young are voters here supporting Robert F. Kennedy Jr.’s independent bid for the presidency. Their political pasts couldn’t be more different.

Hendryx, 67 years old, voted for Donald Trump in 2020. Lamb, 81, cast a ballot for Joe Biden. And Young, 69, said he hasn’t been registered to vote for 50 years—but decided to come out of the political shadows to vote for Kennedy this fall.

The trio show why the effect of Kennedy’s presence in the presidential race is so hard to predict, and why he is causing headaches for both the Democratic president and his opponent, the Republican former president.

The problem for both Trump and Biden: It isn’t exactly clear who Kennedy hurts more, largely because of his eclectic mix of supporters. Most polls of swing states and national surveys show Kennedy pulls slightly more support from Trump, but here in Arizona, a recent Wall Street Journal poll found he snapped up voters equally from both candidates.