Nelson Castro is in trouble.

The Bronx Assemblyman has a negative balance in his campaign account, prosecutors investigating him on allegations he committed election fraud and a newly galvanized county Democratic organization gunning for his seat.

His situation is in many ways similar to that of Maria Baez, who lost her City Council seat after a bruising primary with a party-backed candidate last year. Both Castro and Baez are close allies of José Rivera, who was usurped as county leader by his Assembly colleague Carl Heastie in 2008. Both Castro and Baez have recently come under scrutiny for alleged unethical behavior.

But for Castro, the similarities end there. Whereas Baez suffered from health problems throughout her re-election campaign and was unable to mount a vigorous run, Castro says he is healthy and ready to fight.

“Of course I’m running for re-election,” he said while standing in front of the Paradise Theater, before kicking-off the annual Martin Luther King Day parade down Grand Concourse in the Bronx. “There’s nothing I can do. I can’t quit.”

The county party has taken a different tactic in finding a candidate. Rather than back a politically inexperienced candidate like Fernando Cabrera, who throughout the campaign was forced to answer questions about his residency and party affiliation, the party has chosen Hector Ramirez, a four-term district leader and stalwart Democrat who is well known in the district.

Still, many of the faces behind Ramirez’s campaign will be familiar to anyone who followed Cabrera’s race last year.

“This is definitely part of the same movement,” said Fernando Aquino, a political strategist who worked for Cabrera’s campaign and is now handling communications for Ramirez. “This is part of the change that is going on in the Bronx.”

That message of change reflects a broader understanding that Heastie, in an effort to consolidate his base of support, is targeting elected officials who are seen as incompatible with the new regime.

Ramirez nearly won the seat several years ago. In 2008, former Assembly Member Luis Diaz stepped down to take a job in the Paterson administration and wanted Ramirez to replace him. But then-county chair Rivera tapped Castro to run in the special election, saying he wanted to expand diversity in the borough’s delegation by electing Castro, the first Dominican official from the Bronx. Ramirez, however, is a Dominican as well, and many in the Bronx say that kind of inconsistent behavior from Rivera was a main factor in his downfall.

But Rivera remains influential in Bronx politics, and said he sees no reason for the county organization to target Castro.

“I don’t see where [Castro] has disappointed me in any way,” Rivera said. “It’s a matter of style. I have my own style. Carl Heastie has his own style.”

Party insiders say that challenging Castro has nothing to do with old allegiances or fallout from the county’s leadership changing hands.

“Castro hasn’t worked with the organization that much. He doesn’t have the support of his district leaders,” said one party source. “So that’s a problem.”

Ramirez is already running full-tilt. He boasted to reporters back in November that he would have the support of Bronx Borough President Ruben Diaz, Jr., even though Diaz had not officially endorsed him. A spokesperson for the borough president said in January that there has still yet to be an official endorsement.

Ramirez said that voters care less for the political soap opera that has been playing out in the Bronx than larger issues like jobs and public safety. Nonetheless, Ramirez is already building a case against Castro, portraying him as a scandal-scarred quasi-Republican from Washington Heights who is unfamiliar with the problems in the district.

“The person that is now the incumbent is going from one scandal to another,” Ramirez said. “We can’t continue with this type of representative in Albany.”

Bronx District Attorney Robert Johnson reportedly convened a grand jury last August to look into charges that Castro perjured himself in connection to a voter fraud case from his freshman Assembly campaign in 2008. A spokesperson for the Bronx district attorney would not confirm if an investigation was still ongoing.

But according to Castro, the investigation is over, having produced no evidence of wrongdoing.

“You hear the other team saying I was going to go to jail in two weeks. Then you heard a couple months,” Castro said. “None of it has any weight to it. It’s not going to be a problem.”