Former prime minister Manuel Valls’ endorsement of Emmanuel Macron has widened a split in France’s ruling Socialist Party.

Benoît Hamon, the left’s presidential candidate, has taken Valls to task for going back on his word.

During the Socialist primary, Valls vowed to support his party’s nominee. Now that he has lost the contest, he wants leftwingers to support Macron instead in order to stop Marine Le Pen, the leader of the far-right National Front.

“Traitor”

In response, Hamon has said France must turn the page on “old politics” and “politicians who no longer believe in anything.”

His appeal is not to the pragmatic center but the far left, where Jean-Luc Mélenchon has pushed him into fifth place.

Arnaud Montebourg, a left-wing firebrand who placed third in the Socialist primary, is even more critical, writing on Twitter: “Now everybody knows what a commitment made with honor by a man like Manuel Valls is worth: nothing.”

Other lawmakers have called Valls a “traitor” and a “saboteur”.

Who can beat Le Pen?

But Valls is hardly alone. Dozens of prominent Socialists have endorsed Macron, including Bertrand Delanoë, the former mayor of Paris, and Jean-Yves Le Drian, the incumbent defense minister.

They recognize that Hamon stands little chance in the first voting round later this month.

Since he won the nomination in January, Hamon’s support has only gone down: from a high of 17 percent in the polls to barely 10 percent.

Mélenchon’s popularity has surpassed Hamon’s. The once-fringe candidate has gone up from 12 to 15 percent support.

The two men briefly considered a pact, but now even that couldn’t save the French left. Their combined support would not be enough to best Macron and Le Pen, who are each polling at 25 percent.

The only risk for Macron is that the center-right Republican candidate, François Fillon, manages a comeback. He is currently polling under 20 percent, but was at 25 percent support earlier this year, before news broke that he had paid his family public salaries for seemingly non-existent work.

Whoever qualifies for the runoff against Le Pen is almost certain to beat her. It looks like Macron is the most left-wing candidate who can make it.

Mainstream

It’s not just political expediency that has convinced the likes of Valls to back Macron, however.

Hamon can claim conviction, but his policies are too far to the left of Middle France: He proposes significant tax increases in order to fund a universal basic income.

Macron, on the other hand, is hardly the neoliberal his foes make him out to be. As economy minister from 2014 to 2016, he cut taxes for employers, expanded shopping hours and liberalized intercity transport. Such measures would be uncontroversial in most countries, but they earned Macron the ire of the French left.

Realizing he could never win the party’s presidential nomination, the former investment banker stepped down in August to plot an independent campaign. Given Fillon’s implosion, it is now the last best hope of mainstream France.