"For all of us that have worked so long for change, this is no longer a joke," Bill Samuels told a group of Democratic donors gathered in the living room of cardboard magnate and former candidate for lieutenant governor Dennis Mehiel last Wednesday evening.

Resting on plush couches and standing with glasses of wine were some of the city's most generous reformers-Sarah Kovner, Morris Pearl and Mr. Mehiel's old running mate, Carl McCall.

Mr. Samuels, a Democratic donor who has dedicated the last several years to securing a Democratic majority in the State Senate, had summoned the group here not to push a particular candidate, but to strike one down: State Senator Pedro Espada Jr. of the Bronx.

One year after Mr. Espada threw the State Senate into deadlock-crossing the aisle to join the Republican caucus, only to be lured back a month later by desperate Democrats, willing to make him their majority leader-the party's progressives are trying fitfully to oust Mr. Espada in the September primary, in hopes of freeing the party from his weighty ethical baggage, including a criminal investigation into accusations of embezzlement at the health clinic he founded.

"If Espada wins, it sends a message that we Democrats are continuing to fail," said Mr. Samuels, who has pledged as much as $250,000 to defeat Mr. Espada. He raised the specter that a loss in this low-turnout Bronx district-where Mr. Espada last won the primary with only 4,988 votes-could help deliver the Senate to Republicans, giving them control over redistricting and ultimately threatening the progressive cause at the highest levels.

"Can you imagine losing [Jerry] Nadler or Carolyn Maloney? We don't want that to happen," he said. "This is the most important election. Not attorney general, not even the governor."

"He's got to be defeated this September," declared Bronx councilman and former attorney general Oliver Koppell, whose district overlaps with Mr. Espada's. "If we don't defeat him, we could lose the majority. And we also, in a sense, are losing our soul."

Since his back-and-forth last summer, Mr. Espada has become the poster boy for Albany corruption, defiantly embracing his role as the Senate's spoiler, celebrating the concessions he wrung from his pleading party and doing it all on magazine covers and staged television appearances trumpeting his own power-much to the horror of the liberal establishment.

So, to save its collective soul, the progressive faction is coming at Mr. Espada from all sides.

In early July, the state party-an unofficial extension of Attorney General Andrew Cuomo's gubernatorial campaign-called for Mr. Espada to be de-enrolled from the Bronx Democratic Party. (Mr. Cuomo's running mate, Rochester's mayor, Bob Duffy, was scheduled to headline Mr. Samuels' fund-raiser, but got stuck in Rochester.)

Last week, the Working Families Party-who has seen much of its pro-tenant legislation bottled up in Mr. Espada's housing committee-declared him its first priority and pledged to mobilize its vaunted field operation to knock on 10,000 doors.

And yet, even with a large chunk of Manhattan's money and two political parties allied against him, Mr. Espada could well hang on.

"This is not going to be a wipeout," said Norman Adler, a veteran political consultant who helped a Bronx state senator, Guy Velella, win reelection after an indictment. "It's certainly possible to have all the liabilities that Pedro Espada has and still win an election."

FOR MR. ESPADA, the attention fits nicely into his narrative as an embattled champion of an underdog district, a man who fought his way up from homelessness to establish the successful Soundview health clinic-now the base for his political operations-and has since risen to become the first Latino majority leader in the state's history. In Mr. Espada's telling, it is not the ethical allegations against him but his status as a successful Latino that make him a target of the social and political elite.

"You got to remember, this is a poor district, and they feel victimized," said a longtime Bronx operative who doubts whether Mr. Espada can be beaten this year. "Part of his district is one of the poorest in any urban area. They're looking for heroes."

"It's not like people have as much trust in the accusers," said the operative. "People are skeptical, especially when their district has been disenfranchised for so long. No one in the Bronx is feeling like someone is riding on a white horse to save their asses from Pedro Espada."

Mr. Espada's posturing is slightly complicated by the fact that support finally coalesced last week around a single primary challenger, Gustavo Rivera-a former chief of staff to Andrea Stewart-Cousins and aide to Senator Kirsten Gillibrand-who, like Mr. Espada, was born in Puerto Rico.

Mr. Rivera has lived in the district for a decade, but still lacks a recognizable local profile, leaving him as a largely unknown quantity just seven weeks from primary day.

All of which highlights the importance of organized labor in countering Mr. Espada's name recognition.

Mr. Rivera has ties to 1199 SEIU, which has been one of his biggest donors, and has a particularly large contingent of members in the blue-collar district. And the Working Families Party-which has won big races in other boroughs-is salivating at the chance to be the group that beats Mr. Espada.

"Right now, one of them is assured: Mr. Espada is going to have a good get-out-the-vote operation," said Mr. Adler, the consultant. "The other one is a maybe."

WITH THE LOOMING uncertainty over whether Mr. Espada can actually be beaten, elected leaders are treading lightly with regard to Mr. Espada's candidacy.

On Sunday, before the start of the Dominican Day Parade, Mr. Espada stood in gray pants and a beige guayabera on the Grand Concourse in the Bronx while the rest of the elected officials crowded onto a small stage about 20 feet away.

When the group moved down to the street for a ceremonial ribbon-cutting, an Espada staffer held up a Pedro sign behind the group.

Asked about Mr. Espada, Congressman Jose Serrano of the Bronx-whose son serves alongside him in the State Senate-shrugged. "I'm watching like everybody else is watching."

Mr. Espada-who positioned himself at the beginning of the procession-bounded back and forth, to cheers and waves amid the Dominican flags. He stopped for a few interviews in Spanish, while his supporters handed out bumper stickers. (Mr. Espada declined an interview for this story.)

In case anyone missed him, there was another red-and-white Pedro Espada banner a few hundred feet back, followed by a green Cadillac Escalade with Espada signs.

Mr. Rivera, for his part, was marching along near the 1199 SEIU banner. His campaign manager said people were beginning to recognize Mr. Rivera, and he was encouraged by the lack of campaign literature he had seen discarded on the ground.

Asked how Bronx leaders were reacting to his candidacy, Mr. Rivera was coy. "It's a great day to be marching in a parade in the Bronx," he said.

A minute later, a gale swept through the street, a black cloud overtook the Concourse and the sky opened up, leaving Mr. Rivera to run for cover.

Mr. Espada had already finished the route, under sunny skies.

rpillifant@observer.com