Manchin, who's been falling behind in his campaign against Republican businessman John Raese to complete Byrd's term, said he supports overturning portions of the bill, and wouldn't rule out repealing all of it if a partial strike doesn't correct its problems, The Hill reported Monday.
"The president's plan -- 'Obamacare,' as it's been called -- is far too reaching," Manchin said on Fox News.
"It's overreaching. It needs to have a lot of it repealed. If you can't fix that, repeal the whole thing."
The criticism of President Obama's signature accomplishment this Congress is Manchin's latest effort to put some space between himself and Obama while struggling to keep Byrd's seat in the Democratic fold. Last week, Manchin, governor of a coal-rich state, said Obama was "dead wrong" on both climate policy and support of cap-and-trade legislation.
Raese's campaign accused Manchin of sending mixed messages on healthcare.
Manchin isn't the only Democratic candidate to distance himself from the healthcare law or to advocate changing it, The Hill said.
Alexi Giannoulias, the Democratic nominee in the Illinois race for the U.S. Senate, also called for reforms to the reform legislation.
"I am running on jobs and I'm running on helping small businesses," Giannoulias said on NBC''s "Meet the Press" Sunday, adding the healthcare bill was "far from a perfect vehicle."