Correction: An earlier version of this article misstated West Virginia’s nickname. It is known as the Mountain State, not the Mountaineer State. This version has been corrected.

Sen. John D. Rockefeller (D-W.Va.) at a hearing on Capitol Hill in January. (Susan Walsh/AP)

Sen. John D. Rockefeller IV (D-W.Va.), one of his party’s leading health-care experts, lobbed an accusation this week that most Democrats have only whispered to themselves: some Republicans oppose the new health law because of President Obama’s race.

A retiring senator in his 30th year, Rockefeller made the declaration at an otherwise sleepy committee hearing Wednesday and expanded on the comments Thursday, saying there is an element of prejudice among some Republicans that fuels their opposition to the president.

“It’s only a part,” Rockefeller said of racial elements to the opponents, in an interview with reporters Thursday. “But it is a part of life, and it is a part of American life and world life, and it’s a part of — just a part — of why they oppose absolutely everything that this president does.”

Rockefeller, 76, chose his words carefully after his comments at the Wednesday hearing sparked a fierce reaction from Republicans, particularly Sen. Ron Johnson (R-Wis.), the only GOP senator at the hearing, who accused the senator of playing the “race card.”

A freshman senator and CEO of a plastics manufacturer, Johnson responded that his opposition to the Affordable Care Act was based entirely on how it revamped the health industry. “I didn’t reject this because of the race of the president,” Johnson proclaimed at the hearing. “I rejected this because it’s an assault on our freedom.”

During the hearing, Rockefeller referred to e-mails he had that would demonstrate how race plays a factor in Republican opposition to the health-care law, but on Thursday he declined to elaborate on what he meant.

“Who knows,” he mused.

Once touted as a potential presidential candidate for his health-care expertise, Rockefeller is chairman of the Commerce, Science and Transportation Committee, giving him wide jurisdiction over business. Last year he announced he would retire rather than seek re-election this year, and Rep. Shelley Moore Capito (R-W.Va.) — whose father, Arch Moore, was a longtime rival of the senator’s — is the leading contender to claim his seat.

Over four decades as governor and senator, Rockefeller has seen his state transform from a solid blue Democratic bastion into a deeply red conservative state, at least when it comes to presidential contests. George W. Bush was the first Republican president to win the Mountain State twice since the 1920s, but had to compete hard there in 2000 and 2004.

Obama lost the state in 2008 by 13 percentage points and then by 27 percent in 2012. During the 2012 primary, when a federal inmate was the only other Democrat on the primary ballot, the president received less than 60 percent of the vote.

Many political analysts attribute the shift away from Obama in West Virginia and other Appalachian states to his party’s support of alternative energy production and what some Republicans call a “war on coal.”

Some Democrats believe that racial hostility partly explains the deeply white region’s disdain for the first African American president. Rockefeller is the most senior Democrat to give voice to those feelings.

On Thursday, he declined to say whether his point was directed at voters, GOP officials, or both. He hinted that GOP leaders play into these prejudiced views by mounting a blockade of Obama’s agenda that, according to Rockefeller, is unprecedented.

“Basically, it’s for political reasons that they do that, but at some point, you can’t exclude other things. As they say, everything is on the table,” he said in the brief interview.

Republicans privately seethe at these accusations, often noting the liberals lobbed vicious attacks at Bush over his handling of the Iraq war. They also point out that Republicans actually impeached the previous Democratic president — something they have no intention of doing to Obama.

Johnson, however, blew up at Rockefeller during the hearing: “I found it very offensive that you would basically imply that I’m a racist because I oppose this health-care law. That is outrageous.”

On Thursday Rockefeller made no apology for his remarks. He said he had not spoken again to Johnson. “I certainly haven’t made any effort to,” he said.

He has not spoken to Obama about this issue, either.

“No, I haven’t, nor would I presume to,” he said.