Did the FMLN undermine US-Salvadoran relations for short-term electoral gain?

According to CISPES,

The US government will no longer share confidential financial information with El Salvador in response to former president Mauricio Funes’ public revelation of a report that incriminated former Salvadoran president Francisco Flores in a multi-million dollar corruption scandal. “A decision has been made to stop the flow of confidential financial information from the Treasury Department to El Salvador,” pending further discussions, US Ambassador Mari Carmen Aponte announced on December 5th.

Was it worth it? President Mauricio Funes publicly revealed private information from the US that alleged serious misdeeds by former President Francisco Flores. He did so in late 2013. The news shook El Salvador and nearly propelled Salvadoran Sanchez Ceren and the FMLN to a first round victory over Norman Quijano and the FMLN. It is possible that the FMLN would have lost the runoff election without the damaging information that the US had provided the Salvadoran government.

However, Funes' release of the information damaged relations with the US. The US often shares sensitive financial information with other governments when it's investigating money laundering, embezzlement, and other crimes. However, like any other investigation, the premature release of that information can damage ongoing investigations and perhaps damage the livelihoods of people who might not have been guilty in the first place. Remember, the people are targets of an ongoing investigation.

And what we've seen in El Salvador is that it does not appear that Flores was alone in illegally taking money from the government's coffers. Funes might not only have damaged relations with the US, relations that were already difficult, but he might have undermined investigations that look like they would have brought most of ARENA's top leadership down.