CHICAGO - As the US presidential campaign shifts into high gear, President Barack Obama and Republican candidate Mitt Romney are increasingly attacking each other's views on the country's Medicare program, which is poised to become a major campaign issue.

While the two previously focused their campaigns on the state of the US economy, Romney's choice of Paul Ryan as his running mate has unleashed a new focus on Medicare, the federal program that provides healthcare for the elderly and disabled.

Ryan, a seven-term congressman from Wisconsin, is best known for his role as chairman of the House Budget Committee. As the chairman, he authored two budgets noted for their deep spending cuts and changes to entitlement programs such as Medicare, which he proposed to turn into a voucher program.

Instead of the current Medicare system, in which eligible US citizens receive equal health benefits funded by public taxes, the Ryan budget would provide senior citizens with a set amount of money that could be used to buy health insurance from private companies.

Ryan's supporters praise his Medicare plan as a way to reform the nearly 50-year-old government program, saying his budget's spending cuts are necessary to curb a mounting US deficit. Critics of his plan, however, argue that capping Medicare spending would leave the elderly to make up any of the additional costs on their own, and that it would place a heavy burden on low-income senior citizens, or those with chronic health problems.

In a speech Wednesday in Dubuque, Iowa, Obama slammed Ryan's plan as one that "ends Medicare as we know it," and said it would force seniors to pay extra $6,400 per year in additional healthcare costs.

"My plan reduces the cost of Medicare by cracking down on fraud and waste and subsidies to insurance companies. Their plan makes seniors pay more so they can give another tax cut to millionaires and billionaires," Obama said, referring to the Romney-Ryan ticket.

Since announcing Ryan as his choice for vice president, Romney has tried to somewhat distance himself from the controversial Medicare policies his running mate is best known for, and made an effort to ensure voters of his commitment to the program.

In fact, the Romney campaign chose to go on the offense about the potential Medicare issue, releasing an ad Tuesday that attacked Obama for the $716 billion of cuts made to the program as part of implementing his controversial Affordable Care Act, also known as "Obamacare."

Romney accused Obama of raiding the Medicare trust to fund "Obamacare", and said the Romney-Ryan plan would protect Medicare benefits while strengthening the plan for the next generation.

"My commitment is, if I become president, I'm going to restore that $716 billion to the Medicare trust fund, so that current seniors can know that trust fund is not being raided and we're going to make sure and get Medicare on track to be solvent long-term on a permanent basis," Romney said Wednesday on CBS This Morning.

But Democrats have cried foul at Romney's recent criticism of Obama's Medicare policies, pointing out that the budget crafted by his running mate, Ryan, would also keep in place the $716 billion of cuts to the program.

In the same CBS interview, Romney largely dismissed ideas that his economic plan is identical to Ryan's and that as president he would institute all the policies outlined in the Ryan budget.

"First of all, Congressman Ryan has joined my campaign, and his campaign is my campaign now, and we're on exactly the same page," Romney said. "And my campaign has made it very clear: The president's cuts of $716 billion to Medicare - those cuts are to be restored if I become president and Paul Ryan becomes vice president."

However, the Obama campaign continues to try to make the case to voters that Romney's plan is Ryan's plan - a connection made easier as Romney was quoted earlier this year as calling the Ryan budget "marvelous," and saying it should be passed.

With more than two months left until the US presidential election, both campaigns still have ample time to solidify their message to the American public.

But with the addition of Ryan to the Republican ticket, the political discourse has already begun to shift from the current US economic recovery to Medicare, as well as fundamental differences between Republicans and Democrats on the role of government and spending.

As the majority of Medicare beneficiaries are people over the age of 65, the issue is a major concern to senior citizens, who also have one of the highest rates of voter turnout.