When John McCain's campaign last week pulled out of Michigan—the state New York Times columnist Frank Rich called "ground zero for the collapsed Main Street economy"—it seemed to signal, along with a widening opinion poll gap between the candidates, that the time had come to reassess the "battleground" states in this election. 

True, Barack Obama had earlier redeployed staff from North Dakota to Minnesota and Wisconsin, where their candidate appeared to have a shot at winning. Now, even Karl Rove, architect of George W. Bush's victories, claims that Obama could win if the election were held today—and projections of broad Democratic gains in House and Senate races have implications for whomever moves into the White House in January. 

But despite flexible strategies among the campaigns as they attempt to cobble a "path to 270" (the number of electoral college votes needed for victory), the struggle will center on eight states where hotly contested races as well as some interesting state propositions and ballot initiatives -- some of which involve science and energy policy -- will be in flux up until Election Day. 

Given the margins of error in recent polls, independent voters and those still undecided could still hold the key.

* Data from fivethirtyeight.com show an average of the most recent state-by-state tracking polls.
Averages as of October 10.