U.S. Rep. Stephen Lynch, the lone member of the Bay State delegation to vote against Obama­care four years ago, now predicts the law’s botched roll-out will not only cost Democrats valuable House seats but could even jeopardize their control of the Senate in this year’s hotly contested midterm elections.

“We will lose seats in the House,” the plain-talking South Boston Democrat said in Boston Herald Radio’s studio yesterday, delivering a harsh diagnosis. “I am fairly certain of that based on the poll numbers that are coming out from the more experienced pollsters down there. And I think we may lose the Senate. I think that’s a possibility if things continue to go the way they have been … primarily because of health care.”

Lynch cuttingly questioned whether many of his colleagues who echoed President Obama’s health care promises even “read through the bill really,” noting that many mechanisms created to fund the law still aren’t in effect.

Among them, Lynch said, is a hefty tax on employers who offer so-called “Cadillac” plans that won’t come into play until 2018.

“There’s all these taxes and fees that are the tough medicine, that up to now they haven’t implemented. I don’t know who’s going to do that,” Lynch said. “Maybe … they expect the next administration is going to put these penalties in place. I think that’s the time it’s going to hit the fan.”

The Obamacare fallout has already written the script for Republicans in races nationwide, including in two of New England’s most closely watched bouts.

Former state Sen. Richard Tisei has made it a centerpiece of his push to unseat John Tierney in the 6th District, dubbing Obamacare a “disaster.” Scott Brown has delivered similar slams in his Granite State campaign to oust U.S. Sen. Jeanne Shaheen, whom he’s panned as the law’s deciding vote.

Tisei seized on Lynch’s remarks, praising Lynch in a statement yesterday for “telling the truth about how destructive Obamacare has been” in Massachusetts.

“If I’m elected to Congress, I look forward to working with Rep. Lynch to fix the mess Obamacare has made of our state-based system, which was once touted as the best in the country,” Tisei said.

Longtime Tierney adviser Michael Goldman countered, “While it may be an issue in some places around country, it’s not an issue for Tierney.” He predicted voters will judge Tierney on his “entire legislative issue, not on any single issue.”

Democratic strategist Steve McMahon said the key for Democrats is promoting the law’s popular parts, citing a provision letting parents cover their children until age 26 — even though recent polls show the majority of people look at the law itself negatively. A Gallup poll last week showed 54 percent of Americans disapproved of the Affordable Care Act, compared to 43 percent who approved of it.

“The question for Democrats is they own their vote, they own the bill, and they can’t run away from it. So they need to embrace it and talk about the features people love,” McMahon said. “And there are many.”