Unlocking the Keystone State's politics

— -- Pennsylvania voters go to the polls today to choose between Hillary Rodham Clinton and Barack Obama for the Democratic presidential nomination. It's the biggest prize left of 10 remaining contests. USA TODAY's Kathy Kiely looks at Keystone State politics.

Electoral votes:

21

Delegates at stake:

158 Democrats, more than any of the states yet to vote.

Voting hours:

Polls are open 7 a.m. ET to 8 p.m. ET

Superdelegates:

Twenty-six of the 158 delegates have automatic votes at the national convention. There are 15 pledged to Clinton, five to Obama and six are uncommitted. Gov. Ed Rendell backs Clinton, while Obama's top Keystone State endorser is Sen. Robert Casey. Among the uncommitted: Rep. Robert Brady, who represents part of

Voter registration:

About 4.2 million Democrats; 3.2 million Republicans. More than 217,000 new voters registered this year, most of them as Democrats. The registered voters are a record for a Keystone primary election.

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Demographics:

Pennsylvania is older than the rest of the nation: 15.1% of its people are 65 or older, compared with 12.4% nationally. There are also more people who have served in the Armed Forces: 11.2%, compared with 10.4% nationwide.

The Republicans:

Arizona Sen. John McCain has wrapped up the Republican presidential nomination, but he and Texas Rep. Ron Paul are on the GOP primary ballot. More than 40,000 voters are newly registered as Republicans and about 14,900 changed to the GOP.

Sources: Clinton and Obama campaigns, Pennsylvania Democratic Party, Almanac of American Politics, U.S. Census Bureau, Pennsylvania Department of State. Quinnipiac Poll of 1,027 likely Democratic voters Friday-Sunday; margin of error +/- 3.1 percentage points.

Words chosen not-so-carefully

Obama said he regretted describing jobless Pennsylvanians as "bitter" people who "cling to guns or religion." His words, made during a San Francisco fundraiser, extends a string of campaign gaffes involving the Keystone State. Another example: Former governor Dick Thornburgh's campaign manager, Michele Davis, told the Associated Press that her boss was "the only salvation for this sorry-a— state" during a 1991 Senate race. Thornburgh lost.