US voters head to primary polls; influence of Obama, tea parties to be tested

Update 1: Rand Paul wins Kentucky GOP primary, defeating party favorite in major tea party victory

Update 2: Party-switching Sen. Arlen Specter loses hard-fought primary battle, likely ending his career

Update 3: Democrat Max Critz wins race to fill deceased Pennsylvania Rep. John Murtha's former seat in Congress

US voters cast ballots Tuesday in a handful of key races expected to shed light on how anger at Washington will shape November elections that hold the fate of President Barack Obama's agenda.

Three primaries were expected to test the limits of Obama's influence over the Democratic party's rank-and-file, and the Republican party's ability to harness an internal insurrection from arch-conservative "Tea Party" activists.

And one special election was to shed light on Republican abilities to rally their motivated core supporters to capture conservative districts, key to the party's hopes of retaking the House of Representatives in November.

Those factors are all expected to decide the result of the mid-term elections -- when the sitting US president's party historically loses seats -- which could scuttle key Obama initiatives such as overhauling immigration policy.

In Arkansas and Pennsylvania, two embattled veteran Democratic senators endorsed by Obama, Blanche Lincoln and Arlen Specter, face upstart candidates backed by the party's more left-leaning core supporters.

Monday, White House spokesman Robert Gibbs played down the importance of the primaries, which select each party's candidate for November, saying Obama had followed those races "not that closely" despite helping both campaigns.

Rather than stump for Specter, Obama headed to Ohio Tuesday on a flight which took him 22,000 feet over the heads of Pennsylvania primary voters, according to an AFP reporter on the presidential Air Force One airplane.

In Kentucky, the Republican Party establishment also faces an upset, with polls showing Republican Senate Minority Leader Mitch McConnell's anointed candidate running behind a "Tea Party" favorite.

The three battles come after two powerful long-serving lawmakers, Republican Senator Bob Bennett and Democratic Representative Alan Mollohan, became high-profile casualties of a tide of anti-incumbent mistrust.

In a conservative Pennsylvania House district, Republicans and Democrats will square off for the seat held by the late Democratic Representative John Murtha for 36 years, a race with broad national implications.

Republicans plotting to recapture the House have set their sites on districts, like Murtha's, held by Democrats but captured by the Republican candidate in 2004, 2008, or both.

Defeat could spell trouble for Republicans, who have crowed over a series of polls that show their voters are more energized about the November battle for all 435 House seats, 36 of 100 Senate seats, and 37 of 50 governorships.

Recent national opinion polls have found the US public split on which party should control Congress, but just one in three respondents wants to send their lawmaker back to Washington -- the worst climate for incumbents since 1994.

There were early media reports of low turnout in Pennsylvania, where Specter's fate has been clouded by his April 2009 decision to quit the Republican party and become a Democrat.

Recent polls have shown Democrats Specter and Sestak, a retired vice admiral, running behind Republican hopeful Pat Toomey.

"We'll just have to wait and see how that vote turns out," said Democratic Senate Majority Leader Harry Reid.

In Kentucky, Republican voters appear set to hand "Tea Party" darling Rand Paul the party's Senate nod over McConnell's hand-picked favorite, Trey Grayson, Kentucky's secretary of state.

Paul -- whose father, Republican Representative Ron Paul, ran for president in 2008 -- has openly capitalized on disaffection with Washington, repeatedly urging voters to "send some different Republicans" to the capital.

McConnell, eager to tamp down an internal schism that could harm the party's prospects in November, declined to comment Tuesday on the possible results.

In Arkansas, Lincoln enjoys establishment support, an edge in polls, and a vast money advantage over Lieutenant Governor Bill Halter, whom the party's labor union allies support.

Lincoln has hitched her political fortunes in part to a sweeping bill to reform the rules on Wall Street, pushing for tight curbs on trades in arcane financial instruments called derivatives blamed for fueling the 2008 global economic meltdown.

"It appears very clear to me that Senator Lincoln's going to win," said Reid.

Democrats face an unusual problem in November: Sweeping victories in 2006 and 2008 gave them control over nearly 50 swing districts that could now tilt the other way, handing Republicans the House.