PARIS — Beating a politically weakened former prime minister proved easy for Benoit Hamon, who will represent France’s ruling Socialist Party in the country’s presidential election. Far harder will be convincing voters that his hard-left platform isn’t the recipe for ruin his critics claim.
Hamon’s comfortable victory Sunday in a Socialist primary runoff against Manuel Valls owed much to his radical proposal to give all French adults a regular monthly income to protect them in an automated future where machines will take their jobs.
Hamon’s winning margin — nearly 59 percent of the votes, with about 75 percent of the vote tallied — also appeared as a resounding rejection of unpopular outgoing President Francois Hollande and Valls, his prime minister for more than two years. But the path forward for Hamon is littered with obstacles.
First, he will have to unite the Socialists behind him, which could be heavy lifting. Divisions are deep between the party’s hard-left wing, which consistently criticized Hollande and Valls’s policies, and the advocates of more center-left views.
Another major challenge for Hamon will be negotiating with fiery far-left leader and fellow presidential candidate Jean-Luc Melenchon, who is trying to attract votes from disappointed Socialists. Hamon is proposing a coalition with Melenchon that might have a better chance of winning the general election.
Hamon will also face tough competition from outspoken centrist Emmanuel Macron, who has found increasing popularity with his probusiness views.
Such are the left’s divisions that some Valls supporters may now shift to Macron’s independent run for the presidency.
The outcome of the two-round vote in April and May looks increasingly uncertain.
Leading conservative candidate Francois Fillon, who also is a former prime minister, was rocked in the past week by allegations that his wife, Penelope, held a fake but handsomely paid job as a parliamentary aide. Financial prosecutors are investigating.
At a campaign rally in Paris on Sunday — where a boisterous crowd gave Penelope Fillon a standing ovation and chanted her name, Fillon said, ‘‘We have nothing to hide.’’
A priority for Hamon, a 49-year-old former junior minister and, briefly, education minister, will be to rally the Socialists, split ideologically and wounded by Hollande’s five-year tenure as president.
‘‘Our country needs the left, but a left that is modern and innovates,’’ Hamon said.
Early polling has suggested the Socialist candidate will struggle to advance to the presidential runoff in May, where far-right leader Marine Le Pen could be waiting, campaigning on anti-Europe, anti-immigration and anti-Islam themes.
In defeat, Valls didn’t throw his support behind Hamon, but cautioned against the risk of the country shifting to the right.
‘‘We refuse that tomorrow Marine Le Pen becomes the face of France,’’ he said.