Three words strike fear into the hearts of this cycle’s most endangered House Democrats: Medicare Advantage cuts.

In February, President Barack Obama’s administration proposed cutting from Medicare Advantage as part of the implementation of the Affordable Care Act. Republicans seized on the administration’s announcement and are now plotting to use it to hammer Democrats in the midterm elections this fall.

Seven months from Election Day, angst over the program is pitting the Medicare Advantage’s vulnerable Democratic backers against the party’s more liberal members, many of whom hail from safe districts.

“We’ve strongly encouraged the administration that this is the wrong time to do this, particularly with what’s already happened with the Medicare cuts and the [Affordable Care Act],” Rep. Ami Bera, a California Democrat who faces a tough race in November, told CQ Roll Call last week.

That’s one reason Bera and nearly 60 House Democrats signed a letter urging the Department of Health and Human Services to maintain this year’s spending levels into the next fiscal year.

Medicare Advantage is an alternative to Medicare that is administered through private insurers, although the government subsidizes more per enrollee than under traditional Medicare. It’s a popular program among seniors, who are a key and reliable voting bloc in midterm elections.

The timing couldn’t be worse for vulnerable Democrats, whose electoral fate continues to be tied to the president’s landmark health care law. The Centers for Medicare and Medicaid Services, the government department overseeing the payment rates, is scheduled to release its payment rate on April 7. But the political problem is that open enrollment for Medicare Advantage starts in October, as early voters head to the polls.

“It is surprising that the Obama administration is insisting on these cuts this year despite their obvious unpopularity,” said Dan Conston, spokesman for the center-right group American Action Network, a player in congressional races. “Survey after survey has shown that seniors overwhelmingly oppose the new Medicare Advantage cuts and that it will be effective in galvanizing opposition to Obamacare.”

Conston’s group is already targeting Democrats with advertisements on the proposed cuts in a handful of House and Senate races. Earlier this year, Republicans successfully used the issue in a House special election in Florida district with a large senior population.

“To pay for Obamacare, Washington is forcing seniors to endure deep cuts to Medicare Advantage,” warned the narrator in a U.S. Chamber of Commerce advertisement attacking the Democratic nominee there, Alex Sink, who lost to Republican David Jolly.

Privately, Republicans said polling shows voters often juxtapose Medicare Advantage with Medicare — which means the attacks resonate with seniors who are not even enrolled in Medicare Advantage.

To make matters worse for Democrats, many of the states with competitive House races are also places where, according to the Kaiser Family Foundation, there are an above-the-2013-national-average proportion of Medicare Advantage recipients.

For example, there are several competitive House races in Florida and Arizona — states with sizable elderly populations and some of the highest percentages of Medicare Advantage recipients in the country. Other states with competitive races that also exceed the national average of Medicare Advantage enrollees include Minnesota, California, Nevada, New York and Colorado.

House Democrats must net 17 seats to win the majority. (View our race ratings map at media.cq.com/pub/2013/race-ratings-rc.bit.ly)

Senate Democrats are also vulnerable to Medicare Advantage attacks in 2014. Out of the top crop of competitive Senate races where Democrats are on defense this cycle, Colorado is the only competitive state with above-average Medicare Advantage 2013 rates. But there are indicators that the North Carolina rate jumped year-to-year, which means the issue will likely surface in Sen. Kay Hagan’s re-election, and GOP challengers like Arkansas GOP Rep. Tom Cotton are attacking incumbents such as Democratic Sen. Mark Pryor for voting for the cuts.

Back on Capitol Hill, most Democrats agree that the program has “a math problem,” as one Hill operative put it. In recent years, the federal government spent more per Medicare Advantage enrollee than the regular Medicare recipient.

The ACA sought to bring Medicare Advantage spending rates in line with regular Medicare enrollees. Republicans call the move a “cut” to the program, while most Democrats refer to it as a “savings.”

Many other Democrats have long ripped Medicare Advantage for providing costly extra subsidies to private insurance companies that they contend cherry-pick affluent and healthy seniors. Experts said that the policy is more complex than that. At stake is about $150 billion used to help pay for the health care law in its first decade.

The party’s most vulnerable are not letting the issue go — at least not before November.

Rep. John Barrow, a perennially embattled Georgia Democrat, and Rep. Bill Cassidy, a Louisiana Republican running for Senate, wrote a March 11 letter to Marilyn Tavenner of the Centers for Medicare and Medicaid Services, urging her to “keep the 2015 [Medicare Advantage] payments rates stable at 2014 levels because the proposed cuts will jeopardize beneficiary access to the high quality care these plans provide.”

And 19 of the 24 most vulnerable House Democrats known as Frontline members signed on to the letter. Also, 14 of the 15 most vulnerable House Republicans in the Patriot Program joined the missive. Eight House members seeking the Senate from both parties also signed it.

In the other chamber, Sen. Charles E. Schumer, D-N.Y., spearheaded a similar letter. Between the Barrow and Schumer letters, three of the four campaign committee chairmen signed their chamber’s letter.

Rep. Ron Barber of Arizona, a Democrat whose re-election’s prospects worry his party, went even further, writing an op-ed in Roll Call on the matter.

While there is palpable panic within the Capitol, the people who run national campaigns exude confidence with the party’s political standing on Medicare.

“In the next few weeks, we’ll likely see Republicans once again hypocritically vote for the [Paul D.] Ryan budget that always contains the same Medicare Advantage savings Republicans love to hate,” DCCC spokesman Josh Schwerin said in an email. “Voters know that Republicans can’t be trusted to protect Medicare and we’ll continue to remind them of that at every possible opportunity.”

Although Medicare Advantage’s opponents argue the cuts are necessary, even detractors allow that crossing seniors during a midterm election is a political luxury only afforded to Democrats from safe districts.

A senior House Democratic operative summed it up: “[Medicare Advantage is] bad policy, but it’s turning into horrible politics based on the timing.”

Steven T. Dennis contributed to this report.