MIAMI (CBSMiami) – As both the Republican and Democratic National Conventions near, President Barack Obama maintained a slim lead in three key swing states. Voters also had a message for both candidates, don’t touch Medicare.

According to a new CBS News/NY Times/Quinnipiac University poll, President Obama led Republican challenger Mitt Romney 49-46 percent in Florida, 49-47 percent in Wisconsin, and 50-44 percent in Ohio. The leads in Florida and Ohio were outside the polls margin of error, while Wisconsin was a tie.

Romney received a small boost from selecting Wisconsin Representative Paul Ryan as his vice-presidential running mate, mainly in Ryan’s home state. Previously, Obama led Romney in both Florida and Wisconsin by 6 points.

Part of Romney and Ryan’s problem has been likability. Obama had a 51 percent favorability rating with voters in Ohio and Wisconsin and 50 percent in Florida. Romney was upside down in Ohio with a 45 percent unfavorable rating and 39 percent favorable. Romney was 45-42 favorable in Florida and 44-43 percent favorable in Wisconsin.

Voters in all three states picked Romney to handle the economy, but all said Obama would do a better job handling Medicare. Both issues were rated “extremely important” by voters in all three states. Sixty percent said they favor keeping the current Medicare model.