For all the passion this year's presidential campaign has stirred, a new poll suggests that more than four in 10 voters are still up for grabs.

According to a recent Associated Press-Ipsos poll, 43 percent of registered voters surveyed have not made final decisions on whom to support. That includes 15 percent leaning toward Barack Obama or backing him while saying they could change their minds, and 16 percent tentatively supporting John McCain.

Another 8 percent say they are undecided, and 4 percent weakly back third-party candidates Ralph Nader or Bob Barr.

A poll by the Pew Research Center, conducted in early August and late July, suggests that just three in 10 adults say they are following the campaign very closely.

And in a poll early this month by CBS News, just 18 percent of uncommitted voters said they'd been paying a lot of attention to the race over the last few weeks.

The AP-Ipsos poll was conducted July 31-Aug. 4. It involved telephone interviews with 833 registered voters, for whom the margin of sampling error was plus or minus 3.4 percentage points.