What to Watch in Today's 4 Primaries

Four states go to the polls today, and the results will have huge implications. Politico breaks down what to watch for in each race, and we, as always, provide the cliff notes:

• Pennsylvania: Arlen Specter—the longest serving senator in state history—is in real danger of losing a primary to sophomore Rep. Joe Sestak. There's also a special election for the late John Murtha's seat. His district doesn't lean far right or left, so keep an eye on it as a November barometer.

• Arkansas: The big race is the primary between Blanche Lincoln and challenger Bill Halter—though Halter's campaign admits, “we'll be declaring victory if we bring this race into a runoff.”
• Kentucky: Establishment candidate Trey Grayson has become an unexpected underdog to newcomer Rand Paul—Yes, Ron's son. If he wins, it'll be a victory for Tea Partiers, and a blow to Mitch McConnell's clout.
• Oregon: Former Portland Trailblazer Chris Dudley is the frontrunner in a nine-man GOP gubernatorial primary, but the more conservative Allen Alley could make a late push.

(More Rand Paul stories.)