By Jonathan Allen, CQ Staff

If the early exit poll results are accurate indicators, the Democratic presidential primary contest in Pennsylvania is nip and tuck, with neither New York Sen. Hillary Rodham Clinton nor Illinois Sen. Barack Obama likely to win by a substantial margin.

A swing of a few percentage points in tonight’s vote count can thus make an enormous long-range impact. If Clinton loses, she will face virtually irresistible pressure from fellow Democrats to end her campaign for the Democratic nomination. She trails Obama significantly in pledged delegates and overall popular votes through more than four-fifths of the state-by-state nominating contests. But if Clinton is able to pull out a Pennsylvania victory by a reasonably comfortable margin, she will claim vindication for her oft-stated determination to continue the fight.

The exit poll numbers reported by a variety of media outlets suggest that the political demographics in Pennsylvania are similar to those seen in many previous large-state Democratic contests. Obama, who is seeking to make history as the nation’s first black president, had support from 92 percent of African-American exit poll respondents, while 55 percent of white respondents favored Clinton, according to the Associated Press. Whites were expected to make up about 80 percent of the electorate, with African Americans accounting for about 15 percent.

The Drudge Report, a political Web site, cited a higher 60 percent to 40 percent figure for Clinton among white voters. The difference between winning 55 percent and 60 percent of white voters could be crucial to Clinton’s chances of capturing the state and continuing her campaign.

An analysis by CQ senior writer Greg Giroux — based on a turnout model of 2.1 million voters, with 80 percent white, 15 percent African American and the remaining 5 percent of other races and ethnicities, projects to a 52 percent to 48 percent Clinton victory if she takes 60 percent of the white vote — but a 52 percent to 48 percent Obama win he holds Clinton’s share of the white vote to 55 percent.

Women accounted for 60 percent of voters, according to the Associated Press. Given Clinton’s success among women in past states, that three-fifths proportion of the entire electorate could bode well for the former first lady’s chances not only of victory but of a margin larger than other exit polling might indicate.

Clinton captured 58 percent of voters who made their decision within the last week, according to CNN, a sign, perhaps, that controversies Obama has faced over some of his personal associates and comments he made about working-class voters — about which he was grilled by ABC News moderators in a televised debate last year — may have swayed some voters’ decisions.

Yet two-thirds of voters polled said that Clinton has attacked Obama unfairly, and half said the same was true of Obama’s attacks on Clinton, ABC News reported in its exit poll analysis.

According to ABC, most Democratic voters polled said they expect Obama to be the Democratic nominee. Voters who earn less than $50,000 a year broke 55 percent to 45 percent for Clinton, with Obama winning a similar spread among college graduates, according to FOX News.

Clinton outpolled Obama among gun owners by 58 percent to 42 percent, according to FOX, and Obama won urban voters by 69 percent to 31 percent.