Socialist voters are split between visions of the left in France. Macron, a former banker who served as Economy Minister until last year, is pushing a centrist agenda.
Hamon’s program veers more to the left, and he has broken away from President Francois Hollande, and his government.
Macron’s ideas appear to be more appealing, as he is polling around 25 per cent, compared with about 12 per cent for Hamon.
"Voters who are close to the Socialist party are worried by the fact that Benoit Hamon has taken a more leftist political line,” says Guillaume Caline of the Kantar Public polling agency.
"They also can be reluctant to vote a rebel, someone who has, in a way, betrayed Francois Hollande and his government. And these electors may follow the example of [former Prime Minister] Manuel Valls and other Socialist ministers, and vote for Emmanuel Macron."
Hamon has a base of support, from people who are attracted to his ideas of a universal basic income, and the fact that he made a strong pact he made with the Greens.
His ideas are particularly attractive to young people.
“What really convinces me is his environmental ideas,” said Madeleine, who attended a recent Hamon campaign rally. “It’s not so different from others, but he’s really including it in his program, which is not the case of other programs I’ve seen. It’s really in the core of his ideas. That’s why I’m convinced.”
Pauline, a 24-year-old student, recognizes that Hamon is unlikely to win, but she supports him anyway
“You have to vote for what you believe in, you have to follow your heart,” she says. “All the other candidates want to continue what is happening now. And Hamon wants to change that.”
The far right Front National candidate, Marine Le Pen, looks set to make it into the second round of the election. And polls show now that Macron is the most likely to end up facing her in the second round.
Caline says this might encourage even more people to throw their support behind him, as a “useful vote”: “This temptation of the useful vote may increase in the coming weeks, and may be hard for Benoit Hamon to overcome.”
The big question will be if Hamon supporters and others on the left will be willing to vote for Macron in the second round, or if they will just sit it out.