Patrick Dempsey Shuts Down Senate Buzz Amid Graham Platner Scandal

Patrick Dempsey heard the calls for him to run for Senate ... he just isn't answering them.

The "Grey's Anatomy" star is officially shutting down any speculation he could jump into Maine politics ... revealing in a lengthy open letter Wednesday that he seriously considered a run before deciding his future isn't in Washington ... amid talk over who could replace now-former Democratic Senate nominee Graham Platner.

Dempsey says he gave the idea "real thought" and asked himself whether he could make a meaningful difference in Congress ... but after plenty of soul-searching, he landed on one answer -- no.

Dempsey suddenly found himself in the political conversation after -- as TMZ previously reported -- Platner's campaign was rocked by multiple misconduct allegations. Platner has denied sexual assault claims from one ex-girlfriend ... and has also denied another ex's allegation that he secretly removed condoms during sex without her consent.

Platner officially suspended his campaign on Wednesday night, and party leaders have until July 27 to decide on a replacement candidate.

Rather than launch a campaign of his own, Dempsey says he'll stick with the work that's defined his life off-screen ... helping cancer patients and their loved ones through the Dempsey Center.

His letter -- titled "Why I’m not running for US Senate" published in the Portland Press Herald -- also doubles as a message to whoever ultimately lands the Democratic nomination ... with Dempsey saying Maine deserves a leader who puts service before power, leads with empathy, works across the aisle and tells the truth.