KEANSBURG, N.J.  If you tune in to any of this week’s candidate debates around the country, or watch any of the ads that are beginning to dominate the airwaves, you will hear that next month’s midterm elections are about all the things you probably thought they were about: job losses and federal spending, the health care law and the Obama agenda.

And yet, if Democrats lose their grip on Congress in November, President Obama will become the third consecutive president to see his party tossed from power on his watch  a sequence that has never happened before in the country’s tumultuous political history. This suggests that however much the issues of the moment may seem to be defining these elections, there are some deeper forces at work, too.

A conversation among a group of independent voters in this working-class town may illuminate at least one such longer-term trend.

The fast growth in the number of independent voters  a broad category that includes those who choose not to register with a major party even though they tend to identify with one more than the other, as well as a lot who are skeptical of both  has been making American politics more volatile. According to a Pew Center poll a few weeks ago, the Republican advantage at the moment is mostly grounded in the party’s 13-point lead among independents, which is about the same margin by which those voters supported Democratic candidates in 2006 and Mr. Obama in 2008.