Polls from four key swing states show no big national movement after this summer's widely watched party conventions, and they offer signs that the candidates' handling of economic questions in coming debates could be decisive in the presidential election.

Democratic Sen. Barack Obama holds slight leads over Republican Sen. John McCain in Michigan, Minnesota, Colorado and Wisconsin, where Quinnipiac University conducted new polls in conjunction with The Wall Street Journal and Washingtonpost.com. But his leads aren't commanding, and all the states appear to be in play.

The best news for Sen. Obama in the new surveys may come in Colorado, where he has moved to a lead of four percentage points, 49%-45%, after being down by a percentage point in August. That means he has a chance there to turn a traditionally Republican state in his direction.

Meanwhile, Sen. McCain seems to have a good shot at turning a blue state red in Minnesota, where Sen. Obama leads 47%-45%, which falls within the poll's margin of error.

In Michigan, Sen. Obama holds a four-point edge, 48%-44%. His largest lead is in Wisconsin, where the race stands at 49%-42%.