Health costs have emerged as the top financial anxiety for U.S. households , according to a new survey. It's a dynamic that experts say could pose a threat to the Republican majority in Congress during this year's midterm elections, in which affordability is expected to be a key focus for voters. Two out of 3 Americans surveyed, 66%, are worried about paying for health care — more than other household necessities such as utilities, food and groceries, housing and rent, and gasoline and