PARIS — Beating a politically weakened ex-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 in the three-quarters of polling stations 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 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 pro-business 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 rally in Paris on Sunday – where a crowd gave Penelope Fillon a standing ovation and chanted her name, Fillon said, “We have nothing to hide.”

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