PARIS—After months of soul-searching over the National Front’s decline, Marine Le Pen has proposed a solution: identity politics packaged in a new inclusive brand.

This weekend, Ms. Le Pen hosted Steve Bannon, former chief strategist to President Donald Trump, along with hundreds of party rank-and-file at a National Front congress in northern France at which she railed against immigrants and the global elite. At the same time, she said the party needed to soften its image to strike alliances.

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