WASHINGTON (AP) -- Barack Obama and John McCain start their showdown for the White House as a pair of vulnerable candidates, including real doubts about how each would right a struggling economy, according to exit polls of voters in this year's primaries. The crucial question: Whose weaknesses will cost him the election?
Obama, battling to become the nation's first black president and one of its youngest, cast himself as an agent of change, the quality Democratic voters were seeking more than any other, polls from this year's Democratic primaries showed. In a sharp contrast with his 46-year-old opponent for November, McCain, 71, towered over his Republican rivals as the one with the most experience, according to exit polls from his party's contests.
The two candidates' problems start with the economy, which members of both parties agreed is the country's top issue. Neither man got even half the votes of his party's voters who worried most about the economy.
Compounding their problems: McCain conceded months ago that the economy was not his strong point, while Obama has run weakest with Democratic voters who say they've been hurt by the troubled economy, a growing group.
Each also has other problems to resolve within their party's coalitions.
McCain never did catch on with the GOP's most conservative voters, including those who strongly oppose abortion, are born again or evangelical Christians, or favor tough steps against illegal immigrants. None of those groups, long at the heart of his party, gave much more than a third of their support to the Arizona senator, who has a history of moderate positions on immigration, campaign finance reform and other issues dear to conservatives.
Underscoring his problem with these conservatives: Though McCain scored high for experience, that was a quality only a quarter of Republicans were looking for. Nearly half said they preferred a candidate who shares their values. McCain got only a quarter of those voters.
Obama has done poorly with working-class whites and Hispanics, getting only about one in three of each group's votes overall. He also must win over white Democratic women who have remained fiercely loyal to Clinton, especially those who are middle-aged and over. That will be a delicate task for Obama, who dashed the New York senator's hopes of becoming the nation's first female president this year.
Then there is the matter of race. The Illinois senator, who nailed down the Democratic nomination Tuesday by securing the final convention delegates he needed, will have to navigate the always explosive question of race in America like no presidential candidate before him.
Before he can win the White House, he must cope with a daunting finding: One in seven white voters of his own party said in exit polls that race was important in choosing their candidate. Of that group, not only did two-thirds vote for Clinton, but nearly six in 10 said they would rather vote for McCain in November or stay home than support Obama.
It is possible that even more independent and Republican voters, who tend to be less liberal than Democrats, will consider race when voting. Moreover, pollsters consider it likely that many voters don't tell them exactly what they're thinking on the touchy subject of race, leaving unclear exactly how big a factor it will be in November.
Blacks backed Obama overwhelmingly against Clinton, giving him nearly nine in 10 of their votes. But while they were about one in five voters in this year's Democratic contests, they were just one in 10 in the 2004 presidential election, raising the question: Can Obama increase black turnout?
The same can be asked about voters under 30, six in 10 of whom have backed Obama this year. Historically, they are a notoriously difficult group to get to the polls in November.
Voters 65 and older voters are the age group McCain did best with during the GOP contests and the one where Obama did worst. They historically vote in high proportions in general elections.
Iraq is another major question.
Polls show six in 10 Americans have long opposed the war. That's a seeming advantage to Obama, who has made a withdrawal a major part of his campaign, and a potential problem for McCain, who strongly supports the effort. But a late May poll by the nonpartisan Pew Research Center showed the two running about even on who would make better decisions about the war, as McCain, a Vietnam veteran, has tried to make Iraq a question about who is better qualified to lead a war.
Voting during party primaries is a notoriously tricky predictor of what people will do in the general election, when they are far more focused on their own party identification and the issues.
Underlining that, the Pew survey showed Obama leading McCain slightly for whom was most trusted to handle the economy. It also showed McCain ahead of Obama among whites who have not finished college, 51 percent to 39 percent.
The exit polls point to one test of each candidate's strengths: Independents. Both men ran strongly with that group, who were about a quarter of 2004 general election voters.
The data was based on exit poll interviews with about 44,000 voters in 33 Democratic primaries in which both candidates competed, excluding Tuesday's contests in Montana and South Dakota. It also came from exit polls of 24,000 voters in 27 GOP primaries. The margin of sampling error was plus or minus 1 percentage point for both parties' contests, larger for some subgroups.
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