Washington (CNN) Democratic Sen. Joe Manchin announced Tuesday he won't run for governor of West Virginia in the 2020 election, ending speculation as to whether he would leave the Senate to return to his old job as chief executive.

"I have always said that 'public service is not self-service.' So, when considering whether to run for Governor, I couldn't focus just on which job I enjoyed the most, but on where I could be the most effective for the Mountain State," Manchin said in a statement released Tuesday. "Ultimately, I believe my role as U.S. Senator allows me to position our state for success for the rest of this century."

Manchin had won a tough reelection to his Senate seat in the 2018 midterms , beating his Republican opponent, West Virginia Attorney General Patrick Morrisey, by a little more than 3 percentage points.

Manchin has held the position of West Virginia governor before, first elected in 2004 and reelected in 2008 — which he called the "best job I have ever had."

He left the governor's office and won a special election for the US Senate in 2010, after the death of Sen. Robert Byrd left a vacancy. Manchin won a full Senate term in 2012.

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