IN May 1980, the pollster Richard Wirthlin huddled with his presidential candidate, Ronald Reagan, to plot a course through what looked like a daunting landscape for their party. Just over half the country told pollsters that they were Democrats or leaned that way, compared with just 30 percent that said they were Republicans — a gap that had held steady more or less since the New Deal.

The rest is political history. By winning over millions of white working-class Democrats, Mr. Reagan cut that gap in half and ushered in 26 years of Republican dominance at the voting booth.

Now, on the eve of the midterm elections, surveys show mounting impatience with both the war in Iraq and Republican rule. Some political analysts — including Mr. Wirthlin — say they see a chance for a potential Democratic comeback, an opportunity for another historic realignment of the political parties.