Congress returns to work with Medicare high on the agenda and Senate Republicans under pressure after a barrage of radio and television advertisements blamed them for a 10.6% cut in payments to doctors who care for Medicare patients. How to pay doctors through the federal health insurance program is an issue that lawmakers are forced to confront every year because of what is widely agreed to be an outdated reimbursement formula. But the dispute showcases the continued potency of healthcare issues, which has reached a new level of urgency this year.