Updated 7:39 p.m. ET, 1/8/2014
(CNN) - Sen. Marco Rubio was for the nomination of Judge William Thomas, before he was against him.
Thomas was President Barack Obama's pick for a vacant federal judicial seat in Florida, Rubio's home state. The White House has now pulled the nomination, according to an administration official.
Under arcane rules, a senator can unilaterally block the Senate from considering a nominee from his home state by refusing to return a so-called blue slip.
In light of the Rubio objection, President Obama decided not to renominate Thomas.
Rubio spokesperson Brooke Sammon said on Wednesday the nomination was thoroughly reviewed.
"Senator Rubio has determined that Thomas's record on the state court raises serious concerns about his fitness for a lifetime federal appointment," she said. "Those concerns include questions about his judicial temperament and his willingness to impose appropriate criminal sentences . ... after reviewing Thomas's record, Senator Rubio cannot support moving forward with the nomination," she said.
The move stands in contrast to Rubio's previous support for Thomas.
In a letter signed by Rubio, and first obtained by CNN, the Florida Republican joined with Sen. Bill Nelson, the Democrat who holds the other Florida Senate seat, in endorsing Thomas.
The senators provided White House Counsel Kathryn Ruemmler a list of three names they supported for the vacant judgeship. Judge Thomas was among those names listed. Rubio and Nelson, in their joint letter, said they individually interviewed and had "no objection to any of the finalists."
Thomas was first nominated in November 2012 to a seat on the Miami-based U.S. District Court for the Southern District of Florida. He currently is a state circuit judge for Miami-Dade, first elected to the post in 2005.
Thomas was the only one of 55 pending presidential nominees for various posts whose name was not resubmitted to the Senate last week for confirmation.
The change of heart has raised criticism from liberal legal activists in part because Thomas is highly regarded in the South Florida legal community, and because of his extraordinary personal story.
Born and raised in housing projects in southwestern Pennsylvania, he is the ninth of 10 children raised by a single mother on welfare.
He would have become the first openly gay African-American federal judge, according to supporters.
Rubio's office cited two criminal cases presided over by the judge.
Joel Lebron had his capital case tossed out by Thomas in September 2012. Police said the defendant admitted to participating in the gang rape and murder a decade earlier of an 18-year-old woman in Boca Raton.
But the judge declared a mistrial over testimony from a detective the jury was not supposed to hear from. Prosecutors said the error did not merit a mistrial.
Lebron was tried again, convicted and sentenced to death by the jury. Thomas also presided over the retrial.
Separately, Michele Traverso was convicted of charges related to the 2012 hit-and-run death of a cyclist and served just 264 days of a one-year sentence.
Family and supporters of victim Aaron Cohen - a popular local bicyclist - said the defendant should have faced tougher charges and longer jail time, as much as 15 years under the judge's discretion.
Traverso was charged with and plead guilty to leaving the scene of the accident involving death and bodily harm, and driving with a suspended license.
An assistant who answered a call to Thomas's chambers said he was in court overseeing a trial and unavailable for comment.