Update at 1:55 p.m. ET. Letter Sent To Boehner:

Republican Rep. Henry "Trey" Radel of Florida, Politico writes , "sent a letter on Monday to Speaker John Boehner, R-Ohio, announcing his resignation, saying it 'is my belief that professionally I cannot fully and effectively serve as a United States Representative to the place I love and call home, Southwest Florida.' He said that 2014 has already 'been tremendously positive as I focus on my health, family and faith.' His resignation is effective Monday at 6:30 p.m."

Our original post picks up the story:

Republican Rep. Henry "Trey" Radel of Florida is going to announce Monday that he is resigning from his seat, the congressman's chief of staff tells the News-Press of Fort Myers and The Hill .

Last November, Radel pleaded guilty to misdemeanor cocaine possession. He had been charged with buying $260 worth of the drug from an undercover Drug Enforcement Administration agent.

The freshman congressman was sentenced to one year of supervised probation and fined $250. Radel also agreed to enter a rehab program. He apologized to his family and constituents, and took a leave of absence from Congress. Radel returned to work earlier this month.

As NBC News notes , "Radel's political fortunes ... suffered as a result of the arrest. The Republican Party of Florida had called for the congressman to step down shortly after his arrest, and Radel had drawn a primary challenger in his bid for re-election to his Republican-leaning seat in the House."

Florida's 19th District, which Radel has served, is considered a "safe Republican seat," as the National Journal says . It adds that even before Radel's decision to step aside, jockeying had begun within the GOP among potential successors:

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