Nomination contests for U.S. House and Senate seats concluding Tuesday night in Nebraska and West Virginia begin a key stretch of primaries over the next several weeks that will go a long way toward clarifying November election matchups.
By the end of the month, eight states will hold primaries, along with runoff battles for party nominations in Texas.
Republican primaries are likely to provide clues as to the strength of the establishment wing of the party, compared to the newer and more conservative tea party.
The emergence of Democratic nominees will be watched to determine the strength of the party to hold open offices and possibly take seats from Republicans.
Here is a look at what's ahead in politics for the rest of May:
Nebraska, May 13
With Republican Sen. Mike Johanns of Nebraska stepping down, four Republican heavyweights are vying for the nomination to succeed him.
As rancorous as their primary has grown, no one doubts the eventual winner will be triumphant in November, and Johanns' seat will remain in GOP hands. Recent polls give Midland University President Ben Sasse a lead over rivals Shane Osborn, former state treasurer and U.S. Navy hero, and millionaire banker Sid Dinsdale.
The Republican primary for governor is also crowded and hard-fought. GOP National Committeeman Pete Ricketts has the support of Sarah Palin and other nationally known conservatives, while state Attorney General Jon Bruning is backed by outgoing Gov. David Heineman.
As in the Senate race, it doesn't matter how incendiary the primary for governor gets because the eventual nominee is expected to win handily in November.
West Virginia, May 13
Republican Rep. Shelley Moore Capito is the certain Republican nominee and favorite in the fall for the seat of retiring Democratic Sen. Jay Rockefeller.
The likely Democratic contender is West Virginia Secretary of State Natalie Tennant, a past candidate for governor.
In a state where Barack Obama has been badly beaten in two presidential elections, Tennant is the underdog against Capito, daughter of former three-term GOP Gov. Arch A. Moore.
Capito's 2nd District features a seven-way Republican primary for her open seat. Alex Mooney, former Maryland state senator and Maryland GOP chairman, now lives in the district and has rallied national conservative groups of all stripes to his side. Millionaire pharmacist Ken Reed has been outspending Mooney but lacks his fervent volunteer organization. Democrats have a strong contender in former state party Chairman Nick Casey.
Arkansas, May 20
The shift in Arkansas from Democratic bastion to Republican bailiwick continues. Freshman GOP Rep. Tom Cotton is even money to take out Democratic Sen. Mark Pryor in November, and former GOP Rep. Asa Hutchinson is the favorite to replace term-limited Democratic Gov. Mike Beebe.
In Cotton's 4th District, conservative state Rep. Bruce Westerman is the favorite in the GOP primary. Democrats sense a possible net gain and have rallied behind former director of the Federal Emergency Management Agency James Lee Witt, a close friend and political associate of Bill Clinton.
Republican Rep. Tim Griffin stunned observers by announcing his retirement in the Second District after only two terms, opting instead to run for lieutenant governor. The likely GOP nominee for his seat is establishment candidate French Hill, an investment banker and former George H.W. Bush administration official. Hill will be favored in November over Democrat Patrick Hays, former North Little Rock mayor.
Georgia, May 20
The six-candidate Republican primary for the seat of retiring GOP Sen. Saxby Chambliss is likely to produce a runoff. Unless a candidate in the crowded field wins 50 percent of the vote plus one, the top two vote-getters will meet in a runoff in July.
Final polls point to millionaire David Perdue and Rep. Jack Kingston, both strong conservatives, as the likely top vote-getters. Democrats had been hoping for a Republican nominee with a trail of controversial statements, such as Reps. Phil Gingrey or Paul Broun. Either Perdue or Kingston will be favored in the fall over businesswoman Michelle Nunn, daughter of former Sen. Sam Nunn, D-Ga.
Another heir to a famous name is the certain Democratic nominee for governor: state Sen. Jason Carter, grandson of Jimmy Carter, who is seeking the office his grandfather won in 1970. Polls show young Carter locked in a tight race with Republican Gov. Nathan Deal.
There are spirited Republican primaries for all three of the seats relinquished by GOP House members to run for the Senate. All are expected to remain in Republican hands.
Political pundits are closely watching Gingrey's 11th District in suburban Atlanta, where one of the GOP candidates is former congressman and 2008 Libertarian presidential nominee Bob Barr, and Broun's 10th District in Augusta, where the leading GOP contender is Mike Collins, son of former Rep. Mac Collins.
Idaho, May 20
The rock-em, sock-em primary in the 2nd Congressional District is increasingly billed as the showcase race for the proverbial soul of the Republican Party.
Rep. Mike Simpson, a favorite of the party establishment, faces attorney Bryan Smith, who has the backing of tea party groups and the Club for Growth.
Simpson has out-raised Smith and recently got a boost from Mitt Romney's endorsement in a district where the Mormon population is large.
Oregon, May 20
The surest sign that Democratic Sen. Jeff Merkley may be in political hot water is the intensity of the battle for the Republican nomination to oppose him.
In a state that last elected a Republican senator in 2002, super PACs supporting physician Monica Wehby are duking it out with state Rep. Jason Conger in the GOP primary. Recently, Wehby lent her campaign $5,200 in the last quarter and Conger has used about $20,000 of his own money to jump start his campaign in its final days.
Pennsylvania, May 20
Despite a record of cutting spending and rolling back his state's deficit, Republican Gov. Tom Corbett is still the underdog against any of the four Democrats vying for the nomination to oppose him.
The leading Democratic contender is millionaire businessman Thomas Wolf, former secretary of the state Department of Revenue. Having spent more than $5 million of his personal fortune, Wolf, 65, leads his closest Democratic rival by 20 percentage points.
The two open U.S. House districts are expected to remain in the hands of the party that now holds them.
Republican Rep. Jim Gerlach is stepping down in the 6th District, and his heir apparent is Ryan Costello, chairman of the Chester County Board of Commissioners, who is considered more conservative than Gerlach.
In the 13th District encompassing Montgomery County, where Rep. Allyson Schwartz is leaving to run for governor, the Democratic primary is tantamount to election. The race is crowded and gaining national attention because of the comeback bid of former Rep. Marjorie Margolies, mother-in-law of Chelsea Clinton.
What makes this race particularly intriguing is Bill Clinton's absence on the stump. Family connections aside, Margolies in 1993 cast the deciding vote in the House in favor of Clinton's record-high tax increase and was soundly defeated the following year.
Kentucky, May 20
Possibly the most closely watched race on May 20 is the primary challenge to Senate GOP Leader Mitch McConnell by businessman and tea party favorite Matt Bevin. While no one expects the challenger to win — McConnell leads in the latest Marist Poll by 32 points — the news of the night will be how well the insurgent does.
McConnell faces a stiff battle in the fall from Kentucky Secretary of State Alison Lundergan Grimes. The same Marist poll gives McConnell a 1-point lead over Grimes.
Texas, May 27
When 90-year-old Rep. Ralph Hall fell short of winning a majority in the March 6 GOP primary, pundits began writing his political obituary.
Former U.S. Attorney and runner-up John Ratcliffe had significant backing from the tea party, Club for Growth, and several state legislators. But Hall, who has since turned 91, has come back swinging. With the backing of two former primary foes and all 18 GOP county chairmen, as well as some tea party groups, he is now even money to survive in the 4th District.
The other runoff that bears watching is for the Republican nod for lieutenant governor. State Sen. Dan Patrick, radio-TV commentator and vigorous anti-immigration candidate, stunned observers in the primary by running ahead of two-term incumbent David Dewhurst.
Now many Republicans are having second thoughts about nominating a candidate with a paper trail of controversial statements, and Dewhurst may be back in the game.
John Gizzi is chief political columnist and White House correspondent for Newsmax.
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