A federal investigation into Mayor Bill de Blasio's fundraising is turning into a potential scandal for his administration, and there are new developments regarding the mayor's work to elect Democrats to the state Senate in 2014. NY1's Grace Rauh filed the following report.

Mayor Bill de Blasio is under a microscope. Investigators are examining the mayor's effort to help Democrats take over the state Senate in 2014. A source familiar with the investigation tells NY1 that that the state Board of Elections conducted its own probe and found the mayor's team appears to have deliberately violated campaign finance laws. The board referred the case to the Manhattan district attorney.

Investigators are also looking at his relationship with opponents of the horse-carriage industry. The group leading the campaign to ban the horses says it was subpoenaed by federal and city prosecutors on Thursday.

In an interview on WNYC, the mayor insisted he was embracing the probe.

"I believe everything we did was legal and appropriate and careful. I welcome this being done and being done promptly," he said.

Promptly is the key word. Daily media reports about new developments in the investigation are proving to be a distraction at the very least.

Investigators are looking at the mayor's fundraising more broadly. Additionally, they are trying to understand how and why the city lifted a deed on a Lower East Side health care center, which allowed for the owner to quickly sell it for a $72 million profit.

Political consultant George Arzt says investigations like the ones the mayor is facing can be debilitating for City Hall. Arzt was Mayor Ed Koch's press secretary when the Koch administration was reeling from a massive corruption scandal at the Parking Violations Bureau in 1986.

"We were consumed by the investigations," Arzt said. "It saps the energy of an administration. And it never touched the mayor, obviously, but the mayor was deeply depressed at that time."

As stories about the investigation broke, the mayor may have benefited from an unexpectedly competitive presidential primary in New York that distracted from his own problems. But now that the candidates have moved on, the focus is back on City Hall.