Rep. Charles Rangel (D-N.Y.) is reportedly losing a second Hispanic endorsement to his main Democratic primary challenger, state Sen. Adriano EspaillatAdriano de Jesus Espaillat CabralWe will fight for our DREAMers Influential Latino Dems clash in NY district Rangel challenger concedes MORE.

The New York Post reports, citing an unnamed source, that Bronx Borough President Ruben Diaz Jr. plans to endorse Espaillat in the four-way primary, after previously backing Rangel.

“Ruben has slipped through Charlie’s fingers,” the source said.

He also lost City Council Speaker Melissa Mark-Viverito, who endorsed him in 2012 but is now behind Espaillat.

The endorsement defections are the latest indication Rangel is facing perhaps his toughest fight yet to retain the seat after 22 terms in office.

He defeated Espaillat by just over 1,000 votes last cycle, and will have to again contend with the shadow of his 2010 Ethics Committee censure that still hangs over his record in Congress, as well as Espaillat's charges that he's been in Congress for too long.