Though the new party had little chance of winning the very rich (B.J.P. voters) or the poorest of the poor (Congress’s), the fat layer in the middle is expanding with waves of migration from northeastern provinces. Yogendra Yadav, a soft-spoken political scientist who has become Aam Aadmi’s main strategist, said support for Aam Aadmi had grown fastest among “those who are a little uprooted, who come and are lost for identity, lost for a grouping.”

Those who have latched on to the Common Man bandwagon include many in Delhi’s fast-growing informal economy — “this vast army of drivers, blacksmiths, locksmiths, cobblers, domestic workers, the guys who sell paan on the sidewalk,” said Ashutosh Varshney, a political scientist at Brown University. Voters like these interact constantly with low-level government officials, and their resentment has mounted to the point at which it trumps other political messages.

“There is a certain helplessness that comes from dealing with the malfunctioning state at the street level,” Mr. Varshney said. While more affluent people can “telephone their way through or bribe their way through,” he said, the working poor look to politicians to address their complaints. They vote, and in large numbers.

There are still some gaping holes in the new party’s platform, which is not surprising, considering the group’s swift transformation from a street movement. Though Mr. Kejriwal has pledged that his first major act will be arranging an independent ombudsman to look into complaints against government officials, the party has been slow to issue a clear manifesto beyond opposing corruption.

That has left it unclear where Aam Aadmi stands on basic political and economic questions. Dipankar Gupta, a sociologist, described the party’s appeal as superficial, “another way of saying ‘none of the above.’ ”

As its poll numbers have improved, the party has made compromises that smack of politics as usual, alienating purists who were among its early supporters. On Monday, as Mr. Kejriwal tried to counter a fresh rebuke from Anna Hazare, the Gandhian social activist who was his partner in the anticorruption movement, a man who identified himself as a Hazare supporter sprang up and flung a can of black ink at his face. Party leaders have quietly replaced some of their “common man” candidates with more politically experienced ones.

Mr. Yadav acknowledged that some of those decisions had been painful, but that party leaders had begun to feel “this close to actually making it” and become focused on running candidates who would be seen as viable.