PARIS — He left the corruption scandal-plagued Marine Le Pen of the far-right National Front speechless. He made the nepotism-tarred center-right candidate, François Fillon, grin frigidly, murmuring about a lawsuit. And from the immaculately groomed television anchors he drew only condescending fixed smiles.

It took barely over a minute for Philippe Poutou, a balding and unkempt Ford factory mechanic from Bordeaux running as a fringe candidate in France’s presidential election, to puncture the mutually protective world of the race’s mainstream. Afterward television commentators tut-tutted about his “lack of respect.” That was exactly Mr. Poutou’s point.

So effective was his brutal anti-corruption language that two days after a marathon four-hour debate among all 11 French presidential candidates, the rumpled no-hope candidate of the New Anticapitalist Party was being hailed in some news media here as its unquestioned winner. Mr. Poutou, 50, had instantly become a kind of folk hero, one expressing in unvarnished form what many Frenchmen and women are thinking: The political class, encased in its privileges, is demonstrably corrupt.

The corruption scandals, widely aired in the print press, have been mostly taboo beneath a well-maintained facade of respectability in these debates.