While Mr. Obama’s approval ratings have slid across the board as unemployment remains high, what buoys Democrats are the changing demographics of formerly Republican states like Colorado, where Democrats won a close Senate race in 2010, as well as Virginia and North Carolina.

With growing cities and suburbs, they are populated by increasing numbers of educated and higher-income independents, young voters, Hispanics and African-Americans, many of them alienated by Republicans’ Tea Party agenda…

Virginia, North Carolina and Colorado together have more than double the number of Ohio’s votes in the Electoral College — 37 versus 18. And Obama advisers say that the same demographic factors at play in those states are also present in states Mr. Obama lost in 2008 — like Arizona (whose senior senator, Mr. McCain, was his rival) and Georgia.

Except for Indiana, a long shot, Obama advisers say the president will be favored or competitive everywhere he won before, including Ohio.