PARIS — Far-right leader Marine Le Pen isn’t the only candidate in France’s presidential election vowing to upend the status quo in the European Union.

If far-left firebrand Jean-Luc Mélenchon were to emerge as French president, he has signaled he would seek to overturn the bloc’s foundational relationship: the Franco-German partnership that has underpinned European integration for decades, but which he believes has primarily served Berlin’s interests.

There are still nine months until France’s crucial presidential vote, but Mélenchon’s strong start to his campaign and the infighting among the rest of the left has positioned him as one of the best-placed candidates to challenge Le Pen in a second round, polling shows.