If Republicans are to make the big gains they predict this November, taking over the 40 seats needed to regain control of the House, then upsets will be needed in places once considered untouchable.

This month one untouchable went down: Democrat David Obey announced that he would not run for reelection. Obey has represented the 19,000 square miles of Wisconsin's 7th District since Richard Nixon was president and the Vietnam War was raging-1969. As chairman of the House Appropriations Committee and the prime mover of last year's $787 billion stimulus package, Obey represents the big government mindset that's apparently going out of style among the nation's voters.

Republican Sean Duffy, a 38-year-old district attorney who wasn't even born when Obey first won his seat, was promising Obey the closest race of his career, but potentially faces a close primary contest himself in September.

That change-up came on the heels of an announcement from Gov. Charlie Crist of Florida that he will run as an Independent, rather than face a tough GOP primary race against Marco Rubio for the open seat. Following is a look at 10 other House and Senate primary races worth watching but perhaps worth waiting to predict.

SENATE RACES

Arizona, Aug. 24

After taking considerable ribbing for ditching the label that marked his 2008 presidential campaign, McCain backtracked: "What I was saying is that I have considered myself a person who is a fighter. . . . I fight for the things I believe in, and sometimes that's called a maverick. Sometimes it's called a partisan."

Now with an unexpectedly competitive primary against former congressman J.D. Hayworth, McCain wants the mojo back. He's drifted right on issues like immigration and cap-and-trade as he fights for a seat he's held for almost 25 years. But despite Hayworth's attacks on McCain as less than conservative, McCain has a lead in the polls and support from figures that some conservatives love-particularly vice presidential running mate Sarah Palin.

Colorado, Aug. 10

With friends like Goldman Sachs, Sen. Michael Bennett, D-Colo., may find new enemies: His primary challenger, Andrew Romanoff, is making the embattled investment bank's campaign contributions to Bennett a central battering ram of his campaign against the incumbent. It's helpful ammunition for Romanoff since he and Bennett seem to agree on most political issues. Bennett has said he isn't sure what his campaign will do with the money from Goldman ($6,300), while others have said they will return the company's contributions. If the Romanoff strategy works, it may signal blowback for candidates that voters see as tied to Wall Street.

Kentucky, May 18

Bowling Green ophthalmologist Rand Paul keeps winning new converts to be Kentucky's next senator. On May 3 Focus on the Family founder James Dobson, after receiving assurances of Paul's pro-life bona fides, switched his endorsement from GOP rival Trey Grayson, Kentucky's secretary of state, to Paul. The son of firebrand Texas representative and 2008 presidential underdog Ron Paul has strong ties to the Tea Party movement and has gained a double-digit lead in the race to take over the GOP mantle from retiring Sen. Jim Bunning.

Paul has harnessed his father's considerable fundraising machine to amass more than $2.7 million from a bevy of out-of-state donors. At the same time, he portrays himself as a grassroots political rookie ready to take on federal expansion. Grayson is the GOP establishment's pick-former Vice President Dick Cheney and Senate Minority Leader and fellow Kentuckian Mitch McConnell have endorsed him-which could mean the kiss of death in this election year.

Nevada, June 18

Toppling Senate Majority Leader Harry Reid, the Democrats' top lawmaker, is high on the GOP mid-term wish list. That is why next month's primary features no fewer than five contestants looking to notch a Reid defeat on their political belts. They include a former Miss New Jersey, the son of a famous basketball coach, and an investment banker returning home from New York. Despite the crowded field, a surprise star recently emerged in the race-a chicken. Frontrunner Sue Lowden, the former beauty queen turned anchorwomen turned casino executive, attacked the new healthcare law by suggesting bartering as a payment method for doctor's bills: "In the olden days, our grandparents, they would bring a chicken to the doctor." Comedians like Jay Leno and rivals, even Reid, could not resist: chicken costumes and live fowl began appearing at Lowden's events. But the symbolism behind a Reid defeat is nothing to cluck at. So far Lowden has held her double-digit lead in the polls over top challenger businessman Danny Tarkanian, the son of former University of Nevada Las Vegas coaching legend Jerry Tarkanian. And both are running ahead of Reid in polls.

Pennsylvania, May 18

How is that party switch treating you now, Sen. Specter? The state's longest-serving senator, Arlen Specter, 80, is seeking a sixth term. But this would be his first victory as a Democrat. He abandoned the Republican Party last year to avoid a likely loss in the Republican primary. But now he finds himself in a single-digit fight against U.S. Rep. Joe Sestak, who calls himself the only real Democrat in the race. The home stretch has turned into a typical Northeast brawl: A Specter attack ad declares that Sestak was ousted as a Navy top officer because he had poor command skills. Sestak's response ad accuses Specter of "swift-boating" the former admiral: "Arlen Specter, don't lie about Joe Sestak's record," it says. At an hour-long debate May 1, the contestants feuded over Specter's use of notes at his podium. Specter, who enjoys the backing of the White House and the state's Democratic Party, says switching parties was a return to his roots. But voters don't seem sold yet.

HOUSE RACES

Florida, Aug. 24

Most of the political heat and light in the Sunshine State has come from its wild GOP senate primary, but Florida's 8th District House contest may prove another scorcher: At least seven Republicans are vying to challenge Democratic incumbent Rep. Alan Grayson. The GOP primary winner will also face Peg Dunmire, an official Tea Party candidate in Florida. The race is notable for Grayson's withering assessment of the Tea Party movement. "I can tell you that they should be glad that healthcare reform has mental health coverage, because some of them need it," he told a Florida newspaper. Dunmire's run may draw voters away from the GOP, but political observers agree that the race in the fall will be a close one.

South Carolina, June 8

Rep. Bob Inglis, R-S.C., draws a distinction between his first three terms in Congress (1993-1999) and his second stint that began in 2004. He calls them "Bob 1.0" and "Bob 2.0." In his race to retain one of the most conservative seats in the country, "Bob 2.0" is making the South Carolina primary in the 4th District one of the toughest yet. That's because Bob 2.0 voted against President George W. Bush's troop surge and against drilling in the Arctic National Wildlife Refuge. He's also criticized popular conservative talk show host Glenn Beck and joined six other Republicans in voting to rebuke Rep. Joe Wilson, R-S.C., for shouting "You lie!" at the current president during a joint session of Congress.

Insisting he still has plenty of conservative credentials, Inglis points to votes against healthcare and stimulus spending. But top Republican opponent and county solicitor Trey Gowdy is picking up substantial Republican support.

Alabama, June 1

Incumbent Parker Griffith faces a tough fight in the state's 5th District GOP primary race for an unexpected reason: He's only been a been a Republican since December. Once a Blue Dog Democrat, Griffith angered fellow Democrats with his party switch, but Alabama Republicans weren't exactly awed: Some said he switched to hang onto the seat, making for a tight three-way race with Republicans Mo Brooks and Les Phillip.

Michigan, Aug. 3

Michigan's right-leaning 7th District has changed hands in the last three elections: going moderate Republican, staunch conservative, and then moderate Democrat. Staunch conservative Tim Walberg ("I was Tea Party before there was a Tea Party," he likes to tell reporters) lost the seat in 2008 and wants to take it back from incumbent Democrat Mark Schauer. But first Walberg must take on a political rookie who happens to be both a former Marine and part of the family that owns the Pittsburg Steelers. Brian Rooney moved 30 miles within the state to become eligible for the primary, a decision that has led to a carpetbagger label. But Rooney, whose 1-year-old son was born with a congenital heart defect, said he joined the race over fears of rationing in the new healthcare law. The Iraq War veteran's fresh face has won him the support of county party leaders. If voters decide to embrace the future over the past, then Rooney could join his brother Tom, a freshmen representative from Florida, in Washington.

Virginia, June 8

With Democrat Tom Perriello's victory the closest in the nation in 2008, at a 727-vote margin, many predicted a short congressional stay. And Tea Party nation has descended in force to this moderate-right 5th District: Seven Republicans are embroiled in a primary fight with six professing ties to various unaffiliated Tea Party groups in the district. After Perriello voted for healthcare reform in March, a local Tea Party organizer printed the congressman's home address, encouraging angry voters to drop by. Yet the fact that the organizer actually gave out the address of Perriello's brother appears to be not the only mistake by Tea Partiers, making GOP insider and state Sen. Robert Hurt a likely winner if the Tea Party crowd can't rally around one pick.