McCain's choice of Sarah Palin, an anti-abortion and pro-gun first-term governor from Alaska, as his No. 2 set off a political firestorm that helped stoke conservative enthusiasm for the Republican ticket.

But Zogby said Palin also helped solidify Democratic support for Obama. "For the last few weeks it's been all about Palin and she has been a divisive force," he said. "She has shored up the base for both candidates."

Sarah Palin, Polarizer in Chief.

Obama, who struggled to solidify Democrats in August when just 74 percent backed him, now has the support of 89 percent of Democrats. McCain's support among Republicans grew from 81 percent last month to 89 percent.

....The Illinois senator wiped out McCain's 5-point August lead among independents and expanded his edge over McCain among women, two crucial swing voting blocs in November.

The Reuters poll shows more Obama support among older voters and Catholic voters and an increase for McCain among suburban and small town voters for McCain.