Republican dreams of taking control of the U.S. Senate in November have been declared all but dead over the past several days by prognosticators pointing to trouble facing the party in unexpected places. But a noted analyst of Senate races says much could change between now and Election Day.

In Florida, the ad war centers on Medicare. In New Hampshire, a big topic this week is federal student loans. The ads show how the campaigns are tailoring their message to specific voters in key states.

Democratic and Republican strategists have acknowledged that Paul Ryan's ideas about transforming Medicare may cause problems for the Romney-Ryan ticket among older voters. NPR's Scott Horsley talks with Weekend Edition Sunday guest host Linda Wertheimer about Ryan's trip to Orlando, Fla., Saturday to address his views on Medicare.

By adding Paul Ryan to the GOP ticket, Mitt Romney may risk turning off an important voting bloc: senior citizens. But while some Florida seniors are set against any big changes to Medicare, others are embracing Ryan's plan for reshaping the program.