By allowing Ms. Le Pen to set the agenda, however, Les Républicains have lost their ideological footing. The day after the first round of the elections, on Dec. 6, a desperate Mr. Sarkozy appeared on the evening news, apparently tense and unable to control his nervous tics. He blamed the present government, immigration, the open-border arrangements of the European Union’s Schengen Agreement and “the disappearance of European civilization” — anything but his leadership — for his party’s poor showing.

The man who came back to politics a year ago because he considered himself to be “the best rampart against the National Front” was at a loss to explain why so many of his voters were running away to support Ms. Le Pen and her politics of fear.

Other leaders of Les Républicains have been less charitable. Some of them, like Alain Juppé, another former prime minister who is running for the presidential primaries, have demanded an urgent debate within the party. Leading candidates in the regions, fearful of the effect of Mr. Sarkozy’s divisive tactics, have asked him to stay away from their campaigns. One, Xavier Bertrand, the man who beat Ms. Le Pen in the northern region by uniting the votes against her between the two rounds, even ordered Mr. Sarkozy to “shut up.”

On Sunday night, Mr. Bertrand said that this campaign had “changed forever the way” he was doing politics. A former government minister in Mr. Sarkozy’s administration, he described this election as a “thunderbolt.” He saw it as “the last one before the National Front, maybe, comes to power.” And for that, he blamed “the whole political class,” including himself, for “saying for three decades that it got the message,” while refusing to act. “This is our last chance,” he warned.

The Socialists may be humiliated, but the Républicains are angry, lost and in a state of panic. For the first time since World War II, the xenophobic, euroskeptic far right, which has been steadily growing under Ms. Le Pen’s leadership, has become mainstream.

Where, today, does the right stand in France? What does it stand for? How does it define itself against the anti-immigrant, nativist message of the National Front? What ideology, which strategy will help it regain control of the political agenda before the 2017 presidential election?