ATHENS — Having come out on the winning side of two national votes already this year, Alexis Tsipras would seem to have the mandate he needs to govern Greece.

But it has been a rough-and-tumble eight months since the 41-year-old leftist was first elected, and with his party torn apart by his decision to accept a $97 billion bailout – and the attached conditions – Tsipras gambled in choosing to go back to the voters for a third time.

Rather than strengthening his hand, the vote on Sunday may bounce him from office. In an unexpectedly close contest, polls show that Tsipras’s Syriza Party is barely edging the center-right party ousted in January.

The prospect of a Tsipras defeat makes the vote a critical moment in the evolution of Europe’s anti-austerity left. Syriza’s January victory ushered in the first radical leftist government in the history of the European Union, and like-minded parties are seeking to make their own advances in Spain and Ireland. This month, the hard-line leftist Jeremy Corbyn won the leadership of Britain’s Labour Party.

If Syriza loses, that momentum could be instantly halted.

Governing has been a humbling experience for Tsipras, who made a humiliating about-face in July by accepting harsh bailout terms from Greece’s European creditors just days after the country’s voters heeded his call to reject a similar set of conditions in a national referendum.

The anti-establishment outsider is now in the unusual position of having to defend a deal that he acknowledges will cause pain to Greeks still suffering from an economic collapse that is unparalleled in the developed world since World War II.

“We negotiated with a gun pointed at our heads,” he told an unusually subdued crowd of Syriza faithful on Friday night.

When Tsipras backed down following a long standoff with the creditors, Greek banks were on the verge of default and the country faced expulsion from the euro zone. Those immediate threats have passed.

But Tsipras has been hammered throughout the campaign, both by conservative challengers who say he provoked a confrontation with Europe he had no hope of winning and by former allies who blame him for not going all the way.

“People had the courage to say ‘No’ in the referendum. They felt that we could become masters of our own fate,” said Panagiotis Sotiris, a candidate for Popular Unity, a party composed primarily of dissident former Syriza members. “And then there was capitulation and humiliation. Their hope was betrayed.”

The more serious threat to Tsipras comes from New Democracy, the center-right esparty that has regained favor.