Last Updated Apr 19, 2015 11:33 AM EDT
Sen. Joe Manchin, D-West Virginia, said on CBS News' "Face the Nation" Sunday that he plans to run for re-election to the Senate in 2018 instead of running for governor of West Virginia when the position becomes open in 2016.
Manchin previously served as the governor of West Virginia from 2005 to 2010. He was just two years into his second term when Sen. Robert Byrd died in 2010, leaving an open Senate seat in the state. Manchin said the decision to run for Senate was "the toughest decision of my political life."
"It's a job that I thought we did pretty well. We brought people together, Democrats and Republicans. We put the state of West Virginia before our own politics and we have some pretty good successes with that. I thought maybe I could take that same can-do attitude, that same common-sense approach to Washington," Manchin said. "I will be the first to tell you I didn't think it would be this difficult and it's been challenging but I think we've made some inroads. I really believe we've changed the whole process to a certain extent in the Senate to where we're willing to put our country first and I'm going to continue to fight for that. That's the reason I've made a decision to stay in the United States Senate."
"I know that the Senate's not working the way it was intended to," he added, "but I'm not going to stop fighting to make it work."
He was originally elected in 2010 to fill the remainder of Byrd's term until 2012. He was then elected to a full six-year term.
The current governor of West Virginia, Democrat Earl Ray Tomblin, will have served two terms in 2016 and cannot run for re-election because of term limits.
Manchin is one of the last Democrats representing a predominantly Republican state in the Senate. Several of his colleagues with the same credentials lost their seats during the 2014 midterm elections, including Sens. Mary Landrieu of Louisiana, Mark Pryor of Arkansas and Mark Begich of Alaska.
But he has touted these more moderate members as critical to the functioning of the Senate.
"If we're ever going to change Washington, you have to have moderates whether it be in Democrats or Republicans," Manchin said on "Face the Nation" ahead of the election.
He was also the subject of a small 2016 presidential draft campaign when New Mexico political operative Mike Weber started a @DraftJoeManchin handle on Twitter.
Manchin also weighed in on the framework deal to limit Iran's nuclear program and the 2016 presidential race.
He said he supports a bill that would impose harsh sanctions on Iran if there is no final deal by June 30, but he is not supporting legislation that would give Congress 30 days to review any deal negotiated by the White House and vote on whether or not to lift congressionally mandated sanctions.
"I'd simply rather negotiate for peace and use all our diplomacy than declare war," Manchin said, adding that he has been told the deal would give the international community real inspections over Iran's nuclear program.
"You've got to believe some of the people that have that ability to evaluate. But just going back into the cocoon, and saying, 'We don't trust,' and walk away from this? I don't think there's a senator that doesn't want to be involved in this process. I want to be," he said.
On the 2016 election, he said he supports former Secretary of State Hillary Clinton in her bid for the Democratic nomination.
"I know Hillary Clinton. And I find her to be warm and engaging, compassionate and tough," he said. "She's going to earn every vote. She's working for every vote that she can possibly get. She brings more experience to the table. She's been more on the front lines than any person. More experience than any person we have at that level. She knows the leaders around the world."
Manchin acknowledged, "There's a lot of good people that are showing interest" in the race on both sides of the aisle and that he believes there will be more Democrats who jump into the race. But, he added, "I just personally believe that Hillary is the best prepared to do the job for America."
A previous version of this article said Manchin would run for re-election to the Senate in 2016. His term is up in 2018.