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A retired Army officer who served in Iraq and Afghanistan, Mr. West has a reputation for unabashedly stating his mind. This includes charges that scores of congressional Democrats are communists; labeling Florida Rep. Debbie Wasserman Schultz, who also is Democratic National Committee chair, “vile” and “despicable”; and calling Social Security disability benefits “a form of modern, 21st-century slavery.”

Democrat Patrick Murphy, a political neophyte and construction company executive, has TV spots repeating some of Mr. West’s comments. “Bullying and name-calling has no place in the playground or in Congress,” Mr. Murphy says in one ad as children play behind him.

Though his recent commercials portray him as a loving father and protector of Medicare — a huge issue for South Florida’s many seniors — Mr. West ran a searing ad featuring Mr. Murphy’s mug shot from a teenage arrest outside a South Beach club. Mr. Murphy responded with a spot describing an incident in which Mr. West fired a gun near an Iraqi prisoner’s head and threatened to kill him, after which Mr. West was fined and left the Army.

The two have raised more than $18 million combined, making it one of the country’s most expensive House races, according to the nonpartisan Center for Responsive Politics. But with Mr. West’s ability to raise money from conservatives nationwide, his contributions have outpaced Mr. Murphy’s by 6-to-1.

Their fight also has drawn $3.4 million in spending from outside groups, putting it in the top 20 among House races.

Included is more than $1 million from the House Majority PAC, the campaign committee associated with House Democratic leaders, making Mr. West their top target. He has benefited from $990,000 from the Treasure Coast Jobs Coalition, largely financed by a New Jersey man identified by the Palm Beach Post as a drug company executive.

In Iowa, Mr. King is in the toughest re-election battle of his decade-long congressional career. His vulnerability comes from a redrawn district that leans less Republican than before and a well-financed challenge from the well-known Democrat Christie Vilsack, who is married to U.S. Agriculture Secretary Tom Vilsack, the former Iowa governor.

Tea party voters adore Mr. King for his opposition to the health care overhaul, advocacy of strict immigration enforcement, and opposition to abortion and gay marriage. He’s also known for attention-grabbing statements.

While opposing legislation this summer to make it illegal to watch dog fighting, Mr. King said society’s priorities are wrong if it makes dog fighting illegal but condones people fighting. Those remarks were criticized as a defense of dog fighting and helped prompt the Humane Society to spend nearly $500,000 for an ad criticizing Mr. King, saying, “Those aren’t Iowa values.”

Mr. King says his words are often twisted by opponents he calls “professional hyperventilators.” He has been aided by the National Federation of Independent Business and the House Republican campaign organization, which ran a spot linking Mrs. Vilsack to Mr. Obama. One of Mr. King’s ads shows him in a farm tractor as a man says, “Give me that Iowa straight talker any day.”

In the Chicago area, freshman Mr. Walsh is being challenged by Tammy Duckworth, a former Obama administration official who lost both legs and an arm in Iraq while serving as an Army helicopter pilot.

Mr. Walsh was a political newcomer when he eked out his 2010 victory after a rocky campaign. Shortly after taking office, he released a video in which he said, “President Obama, quit lying,” and he’s accused Mr. Obama of spending money “like a drunken sailor.” He also generated headlines when his ex-wife accused him of missing $117,000 in child support payments, a dispute Mr. Walsh says they resolved.

This year, Mr. Walsh blasted Ms.  Duckworth for being a “failed bureaucrat” and for talking too often about her war experiences. She says that rather than representing his district, Mr. Walsh is “there to serve the tea party, and that simply is not good enough.”

Unlike fellow conservatives Mrs. Bachmann, Mr. West and Mr. King, Mr. Walsh has raised significantly less money than his opponent, unusual for an incumbent. Ms. Duckworth has another advantage — new district boundaries that include far more Democrats.

The new district is also more racially diverse — a problem for Mr. Walsh, who earlier this year said civil rights leader Jesse Jackson would be out of work if blacks “weren’t so dependent upon government.” He also said there are radical Muslims in Chicago’s suburbs “trying to kill Americans every week.”

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