Every even-numbered year, all 435 seats in House of Representatives are up for grabs. The vast majority of seats don't change hands -- 98 percent of incumbents were re-elected in 2000 and 96 percent in 2004.

Interactive: Balance Of Power

That changed in 2006, when Democrats captured 31 seats, turning a 232-202 disadvantage to a 233-202 lead after the election, which has stretched to 235-199 thanks to special elections since the last election.

Democrats defeated 22 Republican incumbents and won eight open Republican-held seats. Republicans won no seats previously held by Democrats.

This year, the popularity of Democratic presidential nominee Sen. Barack Obama could hurt the Republicans, as Democrats seek a veto-proof majority of 270 votes. Of the 32 voluntary retirements from the House, 26 are Republicans, which may open up more seats moving to the Democrats. Five other races have the incumbents not on the ballot: one seat is vacant after the death of Rep. Stephanie Tubbs Jones, D-Ohio, and four incumbents lost in primaries.

2008 House Races
Democratic Retirements
Representative	State
Bud Cramer	Alabama
Mark Udall	Colorado
Tom Allen	Maine
Tom Udall	New Mexico
Michael McNulty	New York
Darlene Hooley	Oregon
Republican Retirements
Terry Everett	Alabama
Rick Renzi	Arizona
John Doolittle	California
Duncan Hunter	California
Tom Tancredo	Colorado
Dave Weldon	Florida
Jerry Weller	Illinois
Ray LaHood	Illinois
Ron Lewis	Kentucky
Jim McCrery	Louisiana
Jim Ramstad	Minnesota
Chip Pickering	Mississippi
Kelly Hulshof	Missouri
Jim Saxton	New Jersey
Mike Ferguson	New Jersey
Heather Wilson	New Mexico
Steve Pearce	New Mexico
Vito Fossella	New York
Jim Walsh	New York
Tom Reynolds	New York
Dave Hobson	Ohio
Deb Pryce	Ohio
Ralph Regula	Ohio
John Peterson	Pennsylvania
Tom Davis	Virginia
Barbara Cubin	Wyoming
Source: The Cook Political Report

According to CQpolitics.com, 328 of the 435 races are likely "safe" -- 201 Democrats keeping their seats and holding onto Tubbs Jones' seat and 126 Republicans keeping their seats.

The potential pitfall for Republicans are the seats where there is no clear favorite, or lean one way or another.

Of the 23 tight races with no clear favorite, 17 are seats currently held by Republicans, versus six held by Democrats.

Of the races that lean to one party or another, 23 of the 24 races with a Republican favored are GOP-held seats, where 13 of 19 races favoring a Democrat are seats the party currently holds.

One of those races is for Alaska's at-large seat, where 18-term Rep. Don Young, a Republican, is being closely challenged by Ethan Berkowitz, the former minority leader in the Alaska State House of Representatives.

Young barely survived a challenge from the state's Lt. Gov. Sean Parnell -- who had the backing of Gov. Sarah Palin, the Republican Party's nominee for vice president -- winning by 309 votes. An Ivan Moore Research poll has Berkowitz leading 8 points.

The lone Democratic seat that leans Republican is that of Florida Rep. Tim Mahoney in Florida's 16th District.

Mahoney won the seat in 2006 by a 50-48 margin and was going to face a tough re-election fight from Tom Rooney, CQ Politics reported. Mahoney has also been fighting a scandal involving an alleged extra-marital affair that came to light in October.

One of the seats that is still considered a Republican lean that has gotten significant national attention recently is in Minnesota, where first-term Rep. Michele Bachmann faces Democratic challenger Elwyn Tinklenberg.

Bachmann, on an MSNBC political show on Oct. 17, suggested that Obama might have anti-American views and supported an "expose" that looked at which members of Congress were pro-American or not.

"What I would say is that the news media should do a penetrating expose and take a look. I wish they would. I wish the American media would take a great look at the views of the people in Congress and find out if they are pro-America or anti-America," Bachmann said.

Since Bachmann's comments, Tinklenberg has raised more than $1.3 million from across the country, and the National Republican Congressional Committee has stopped advertising for Bachmann, the Minneapolis Star Tribune reported.

Two separate polls have Tinklenberg pulling into a small lead and within the margin for error.

CQ Politics has determined that of the 41 races where one party is favored over another, none of the 25-Republican favored seats is currently held by the Democrats. Of the 16 seats Democrats are favored to win, two are GOP seats.