WINDHAM, N.H. (AP) — President Barack Obama sharply criticized rival Mitt Romney and his running mate Paul Ryan on Medicare, saying the Republican challengers would alter the health care system for older Americans by making them pay more so wealthy taxpayers can get a tax break.

Obama made his remarks while in New Hampshire, a competitive state in the presidential contest. Romney and Ryan will campaign in the state Monday.

Since Ryan, the chief House Republican budget writer, joined the ticket, Medicare has taken prominence in the campaign.

Obama said Romney wants to give seniors a voucher to buy their own insurance and cited analyses that say older Americans could end up paying $6,400 more a year.