Republican presidential candidate Mitt Romney‘s campaign is on the offensive over health care reform as Democrats make a concerted effort to attack Romney’s choice for vice president, Rep. Paul Ryan, as a threat to seniors.

Shortly after Romney’s announcement that Ryan would be his candidate for the vice presidency, the Democrats began highlighting a Medicare theme. The Romney campaign, however, was quick to reply, saying that the Democrats are the real threat to seniors.

“There is only one person in this race who has already cut Medicare for seniors, and that is President [Barack] Obama,” declared a statement from Ryan Williams, a Romney spokesman.

“Obamacare cut Medicare for America’s seniors by $700 billion [but] Mitt Romney and Paul Ryan have a bipartisan plan to strengthen Medicare for today and tomorrow’s seniors,” the statement continued.

The statement was in response to Democratic attacks.

“FACT: Paul Ryan would end Medicare as we know it by turning it into a voucher program, costing seniors up to $6,350 a year… FACT: Paul Ryan cosponsored a bill that would ban many common forms of birth control, including certain birth control pills.,” alleged tweets from Obama’s campaign office.

“Congressman Paul Ryan led House Republicans in voting to end the Medicare guarantee, which increases costs on seniors and weakens America’s great middle class in order to give tax breaks to millionaires,” read a Saturday statement from the House Minority Leader Rep. Nancy Pelosi.

“With Mitt Romney’s support, Ryan would end Medicare as we know it and slash the investments we need to keep our economy growing — all while cutting taxes for those at the very top,” read a fundraising appeal sent out by Obama campaign manager Jim Messina.

The fight over Medicare’s future is a critical battleground, because seniors are an important swing-voting block and are very familiar with Democratic charges that the GOP plans to attack their health care programs.

Some Democrats believe their tactics on Medicare helped some of their candidates survive the Democrat’s 2010 electoral disaster, and can help Obama win Florida, Ohio and other must-win states for the presidential election.

The next few weeks will likely see a series of TV ads, polls and coordinated statements arguing that Ryan’s plan is a threat to seniors.

But Ryan is also familiar with the Democrats’ pitch, and has plenty of practice explaining how his Medicare reform proposal would allow people older than 55 to continue with the current Medicare program despite its rapidly rising costs.

His main proposal would asks future retirees to join the Medicare program, or use a government “premium support” check to buy commercial health care services.

Ryan also gets to argue that reform for premium support has been backed by Democrats, such as Oregon Sen. Ron Wyden, and that the funds for the existing Medicare program are already being drained to fund Obamacare.

In July, the Congressional Budget Office reported that Obamacare will slice $716 billion from Medicare over the next 10 years.

But progressives are determined to portray Ryan’s Medicare reform proposal as a mortal threat to seniors — an attempt to “voucherize” the program and “end Medicare as we know it.”

Romney “has chosen Paul Ryan, who proudly proposes forcing millions of seniors into poverty by ending Medicare as we know it, as his running mate,” read a statement from Lee Saunders, president of the American Federation of State, County and Municipal Employees union of government workers. “Mitt Romney and Paul Ryan are plotting a nightmare for middle-class families.”

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