The end to the soap opera in South Carolina, liberals on the warpath in Arkansas, and California tea partiers seek to flex their muscles. Those are some of the storylines today as 10 states will go to the polls to choose party nominees.

Charles Mahtesian of Politico has some races to watch, including the bellweather race for the Democratic primary for senate in Arkansas:

With Democratic Sen. Blanche Lincoln's career on the line, this one easily rates as the day's marquee Senate contest.

Sure, this race is about ambition - no one has ever described Lt. Gov. Bill Halter otherwise - but the real story of the runoff is in its implications for Democratic centrists across the nation.

Fueled by progressive support, Halter's campaign accelerated from zero to 60 in almost no time, rapidly closing the gap on a well-funded, scandal-free two-term incumbent who carried the White House imprimatur.

Whether Halter topples Lincoln or not - he had a slight edge in the most recent poll - the lesson many moderates will take from Arkansas is clear: Don't mess with the left.

Lincoln has been all over the map ideologically which has angered liberals who demand lock step obedience. You can never be too far left for the leftists and Lincoln has sought a middle ground on some issues.

Her main challenger is a the kind of Bill Clinton Democrat Arkansas voters seem to like; a populist, liberal on economic policies while somewhat conservative socially. Halter also has SEIU help as well as teachers giving massive aid to his campaign.

Other big races include the South Carolina GOP governor's primary where Nikki Haley maintains a wide lead despite allegations of infidelity, and the Nevada GOP senate primary that will choose a candidate to take on a weakened Harry Reid. The hugely expensive California primaries will also come to an end today with GOP chances in both the senate and governor races better than they have been in the recent past.