Today, the last big Senate primaries before November will be held in Delaware and New Hampshire, capping off a sometimes turbulent season of intra-party contests, mostly for the GOP.
In New Hampshire, two conservatives will battle on the Republican side as Attorney General Kelly Ayotte faces attorney Ovide Lamontagne. Both are Tea Party-ish enough to split the endorsements of Sarah Palin, who is backing Ayotte, and South Carolina Sen. Jim DeMint, who is backing Lamontagne.
A highly anticipated race is unfolding in Delaware, as conservative Christine O'Donnell is making a competitive run at the long-time frontrunner in this race, centrist Congressman Mike Castle. With the sudden backing and financial support of Tea Party Express, which endorsed O'Donnell two weeks ago, O'Donnell has gone from being virtually unknown outside the state to running neck-and-neck with Castle, according to a poll released Monday by Public Policy Polling.
These contests follow a handful of primaries in which Republican candidates with Tea Party-style policy agendas have toppled establishment picks who were long considered, in their respective races, to be the GOP's best hopes.
The trend began this April, when upstart conservative Marco Rubio forced popular Gov. Charlie Crist to leave the GOP. Crist had been endorsed by the GOP's Senate campaign arm, the National Republican Senatorial Committee (NRSC) in early 2009, when he was the most (and perhaps the only) promising Senate candidate Republicans had coming out of the disastrous 2008 election cycle.
It continued in May when Rand Paul defeated Secretary of State Trey Grayson in Kentucky, despite Senate Minority Leader Mitch McConnell's backing of Grayson, and when Sen. Bob Bennett was knocked off his re-election ballot by two Tea Party candidates at the Utah state convention. In June, Sharron Angle proceeded to defeat former state Republican chairwoman Sue Lowden in Nevada, becoming one of the most prominent Senate candidates the Tea Party movement has produced.
August saw the biggest primary upset of all when attorney Joe Miller defeated incumbent Sen. Lisa Murkowski in Alaska, after another Tea Partier, district attorney Ken Buck, knocked off establishment-preferred former Lt. Gov. Jane Norton in Colorado.
If today's Delaware race goes to the Tea Partier O'Donnell, it would be the seventh primary race in which an insurgent, Tea-Party-style conservative supplanted an establishment frontrunner.
In some of these states, Republicans could almost care less who their nominee is. In Utah, Bennett's demise does not portend a Democratic victory. In Alaska, Miller's win may have given Democrats a better chance at picking up the seat, but he's still expected to win.
In other states, Democrats are hoping Republican upsets will work more directly in their favor. Most observers expected Crist, for instance, to deliver a sure victory for Republicans in Florida; now that Rubio has supplanted him on the GOP ticket, it's about 50/50 whether Crist will win as an independent, and if he does some wonder if he'll caucus with Democrats in the Senate.
The NRSC didn't officially endorse in any of these races except for Florida, where it backed Crist. Nor, it says, did it spend any money in support of the establishment candidates. And it points out that Tea Party enthusiasm is also good for the party.
"A product of the primaries has also been voter enthusiasm on our side," said NRSC spokesman Brian Walsh. "We've had four million more Republicans vote this year than Democrats, and that's a swing from 2006 when 3 million more Democrats voted than Republicans."
DC Republicans have a rocky relationship with at least one of these insurgent campaigns: Miller complained when the NRSC sent a lawyer to Alaska as absentee ballots were counted in the days following Miller's election-night win. In Florida, on the other hand, fences appear to be mended with Crist out of the party.
Democrats have had their issues, too. In Illinois, Alexi Giannoulias emerged as the party's Senate candidate despite the White House's reticence to support him. By mid-summer, primaries had forced the DSCC to spend $1.8 million in Colorado, Pennsylvania, and North Carolina. Liberal candidates mounted challenges to DSCC-backed Sens. Blanche Lincoln, Michael Bennet*, and Arlen Specter in Arkansas, Colorado, and Pennsylvania. Specter lost out to Rep. Joe Sestak. DSCC-backed Rep. Kendrick Meek repelled a surprise challenge from billionaire Jeff Greene in Florida, who blanketed the airwaves with negative ads about Meek. In North Carolina, Cal Cunninham lost to Elaine Marshall despite the DSCC's help.
Questions of party unity have been raised for Republicans, and Democrats could experience similar pangs in a couple states. Asked about lingering primary divisions, a GOP strategist said, "Come October, this is not what people are going to be talking about. Everyone is united behind trying to win a seat."
The questions hanging over election season now are: Will the emergence of conservative, Tea-Party-backed candidates cost Republicans a few Senate seats on Election Day? How will the parties spend their resources? What tough decisions will be made about which candidates are worth spending money on?
After Delaware and New Hampshire are done with tonight, the rosters will be solidified, the parties will have messy primaries behind them, and general election season will begin.
*Full disclosure: Bennet is the brother of Atlantic editor James Bennet.
Chris Good is a political reporter for ABC News. He was previously an associate editor at The Atlantic and a reporter for The Hill.