President Barack Obama is holding on to his lead in Ohio, but he now faces tighter races in Florida and Wisconsin, a Quinnipiac University/CBS News/New York Times poll out Thursday shows.

Voters in all three battleground states give favorable ratings to Paul Ryan, but Ryan's Medicare plan is opposed by majorities of voters. Obama is viewed as better at handling Medicare than Mitt Romney in all three states, the poll shows.

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Here's how the new poll of likely voters compares to earlier Quinnipiac University/CBS News/New York Times polls:

Ohio: Obama is at 50 percent, which is what the poll on Aug. 1 showed, compared to Romney's 44 percent in both polls.

Florida: Obama has slipped to 49 percent from 51 percent in the Aug. 1 poll, while Romney is now at 46 percent compared to 45 percent in the Aug. 1 poll.

Wisconsin: Obama has dropped to 49 percent from the 51 percent he had in an Aug. 8 poll, and Romney has inched up to 47 percent from 45 percent in the Aug. 8 poll.

"It seems like the pick of Paul Ryan has had some small beneficial effect for Mitt Romney," Peter Brown, the assistant director of the Quinnipiac poll, told CBS News' Bill Plante on "Face to Face". Referring specifically to Wisconsin, Brown added, "Obviously, it's had some home-team effect."

The latest poll showed that Ryan is unknown to about four in 10 likely voters in Florida and Ohio, and obviously most familiar to Wisconsin voters.

Medicare ranks as the No. 3 issue for likely voters in all three states, with the economy and health care coming in first and second, according to poll. About 6 in 10 likely voters in each state want Medicare to continue operating as it presently does, and fewer than a third of those polled said Medicare should be changed to a system in which the government provides money for buying health insurance or Medicare insurance, as Romney has proposed.

The poll was conducted by telephone August 15-21. The number of likely voters interviewed in each state was 1,241 in Florida, 1,253 in Ohio and 1,190 in Wisconsin. The margin of error in each state is plus or minus three percentage points.