By Greg Giroux, CQ Staff

Raising enough money is one of the biggest obstacles for congressional candidates who trying to unseat incumbents. They have to compete with sitting office holders who already wield fundraising clout and enjoy other benefits of incumbency.

But some challengers do raise enough money to at least run competitively. That is expected of most of the 10 top fundraisers among this year’s candidates who are challenging incumbents of the opposite party, listed below.

This list, the result of a CQ Politics analysis of candidates’ year-end 2007 campaign finance reports filed recently with the Federal Election Commission (FEC), makes one thing clear. If you want to raise big bucks to run for the U.S. House, it helps to have done so before. Six of the 10 challenger candidates who reported the most overall receipts in 2007 were candidates for Congress in 2006, as were four of the candidates who reported having the most cash on hand as 2008 began.

If you’re a first-time congressional challenger, it can help to have served in state or local office, with experience in building networks of political supporters who can give money and assist in the raising of even more campaign cash. Other challengers have had successful careers in business and/or law — and have bulging phone directories of friends and associates who they can tap for donations up to the legal maximum of $2,300 per election. A good word or an endorsement from political party officials, interest groups and organizations of ideological activists can help too.

The list immediately below shows those opposite-party challengers who lead in overall fundraising. Below that is the list of the 10 challenger candidates who had to most remaining campaign cash on hand. Total receipts can include money that the candidate has given to his or her campaign in the form of personal loans or contributions.

CQ Politics previously examined the 10 best-funded House candidates in three other categories: those running for open and vacant House seats; those challenging incumbents in primary elections; and incumbents seeking re-election.

U.S. House Candidates challenging incumbents of the opposite party who reported the most total receipts in 2007

1) Alexander “Sandy” Treadwell, Republican, New York’s 20th District ($1.24 million)

Treadwell, a former chairman of his state’s Republican Party, has basically matched with personal funds the $620,000 he reported raising from individuals and political committees. He’s taking on an exceptionally well-funded incumbent in freshman Democrat Kirsten Gillibrand , who reported raising more money in 2007 than all but one other member of the House.

2) Deborah Honeycutt, Republican, Georgia’s 13th ($1.1 million)

Honeycutt, a physician, is seeking a rematch of a 2006 campaign in which she lost decisively, 69 percent to 31 percent, to Democratic Rep. David Scott . Her large receipts total comes with a very big caveat. Honeycutt spent $200,000 to raise money through expensive direct mail fundraising solicitations. Though these appeals brought in more than she spent in the fourth quarter of 2007, they left her with a modest cash-on-hand total of $124,000.

3) Jim Ryun, Republican, Kansas’ 2nd ($1.08 million)

Ryun hasn’t had trouble raising money as a former incumbent, though he was defeated in a 2006 rematch by Democrat he is challenging this year — Nancy Boyda — in a generally Republican-voting district in and around Topeka. Ryun defeated Boyda in 2004, so this year’s race would be a “best two out of three” matchup. But that will occur only if Ryun can defeat Kansas state Treasurer Lynn Jenkins in the Aug. 5 Republican primary. Jenkins reported $514,000 in total receipts and $416,000 in available cash. Boyda, meanwhile, raised $766,000 in 2007 and had $654,000 left to spend.

4) Kay Barnes, Democrat, Missouri’s 6th ($1 million)

Barnes has fundraising clout because she is a former mayor of Kansas City, part of which is included in the northwestern Missouri district that Republican Rep. Sam Graves is defending. Barnes, the presumptive Democratic nominee, is a strong recruit in a district where the Democrats didn’t vigorously compete in recent election cycles.

5) Jim Himes, Democrat, Connecticut’s 4th ($951,000)

Himes, who has a background in investment banking, is the leading Democratic candidate against 10-term Republican Rep. Christopher Shays . The incumbent narrowly won re-election in 2006, staving off a Democratic wave in the six-state New England region that left him its only current House Republican. More than 93 percent of Himes’ total receipts came from individual donors, so he hasn’t really tapped political action committees or his own wealth yet.

6) Dan Seals, Democrat, Illinois’ 10th ($900,000)

Seals, a business consultant, earned a rematch of his close 2006 contest with four-term Republican Rep. Mark Steven Kirk with an overwhelming victory in the Feb. 5 Democratic primary election. Seals looks to be even better-funded than in 2006, when he raised about $2 million despite limited assistance from the national Democratic Party and ended up with 47 percent of the vote — a very respectable showing against Kirk, a popular centrist. Seals actually raised more in 2007, the year before the 2008 general election, than he raised for his previous campaign through June 2006, midway through that election year.

7) Darcy Burner, Democrat, Washington’s 8th ($874,000)

Burner, a former Microsoft manager, is taking on two-term Republican Rep. Dave Reichert in a rematch of a very close 2006 race that the congressman won by 3 percentage points. Burner’s fourth-quarter donors included political committees associated with some labor unions and top House Democrats including Majority Leader Steny H. Hoyer of Maryland; Chris Van Hollen , another Maryland representative, who chairs the Democratic Congressional Campaign Committee; and Debbie Wasserman Schultz of Florida.

8) Shelley Sekula Gibbs, Republican, Texas’ 22nd ($870,000)

Sekula Gibbs is one of 10 Republicans vying in the March 4 primary for the nomination to challenge Democratic Rep. Nick Lampson . The incumbent, who formerly served 10 years in another Texas district, was elected in November 2006 to the Houston-area seat that Republican Tom DeLay had vacated upon his resignation that June. But Lampson technically succeeded Sekula Gibbs, who lost the full-term race to Lampson but won a simultaneous special election to serve the remaining two months of DeLay’s unexpired term (in which Lampson did not compete).

9) Francisco “Quico” Canseco, Republican, Texas’ 23rd ($850,000)

Most of Canseco’s receipts have come in the form of loans from the candidate’s personal accounts. Canseco, a lawyer, is challenging Democratic Rep. Ciro D. Rodriguez in a politically competitive district that includes part of San Antonio and more than 700 miles of country that follows the Rio Grande along the border with Mexico. Lyle Larson, an elected commissioner in the county that includes San Antonio, opposes Canseco in the March 4 primary.

10) Christine Jennings, Democrat, Florida’s 13th ($810,000)

Jennings is seeking a rematch against Republican Rep. Vern Buchanan , who won an open-seat 2006 race by 369 votes. Jennings challenged the results, arguing that there were voting machine malfunctions that affected the outcome. But a bipartisan task force recommended Feb. 8 that the House Administration Committee dismiss her challenge, after the Government Accountability Office didn’t discover any malfunctions in the electronic voting machines that were used in Sarasota County.

Jennings’ total receipts include monies she received in calendar year 2007 that were technically collected by her 2006 campaign committee. Jennings last July formed a new campaign committee, Jennings 2008, that collected $481,000 through the end of last year.

Buchanan is among the best-funded House Republican incumbents, with $1.9 million in 2007 receipts and $1.1 million in the bank. In 2006, Buchanan, a wealthy auto dealer, ran a largely self-financed campaign that spent $8.1 million, the most among all House candidates, including incumbents.

U.S. House Candidates challenging incumbents of the opposite party who had the most cash-on-hand as of Dec. 31

1) Jim Himes, Democrat, Connecticut’s 4th ($800,000)

Himes is listed above as the fifth-leading challenger fundraiser.

2) Alexander “Sandy” Treadwell, Republican, New York’s 20th ($755,000)

Treadwell is listed above as the leading challenger fundraiser.

3. Kay Barnes, Democrat, Missouri’s 6th ($743,000)

Barnes is listed above as the fourth-leading challenger fundraiser.

4) Dan Seals, Democrat, Illinois’ 10th ($627,000)

Seals, listed above as the sixth-leading challenger fundraiser, didn’t deplete his cash reserves by running pricey television or radio ads during his recent primary campaign because he held an overwhelmingly lead over challenger Jay Footlik, who took just 19 percent of the vote. Seals needs to save as much money as he can for his general election campaign against Kirk, who is among the best-funded members of Congress.

5) Darcy Burner, Democrat, Washington’s 8th ($607,000)

Burner is listed above as the seventh-leading challenger fundraiser.

6) Robert Lord, Democrat, Arizona’s 3rd ($503,000). Lord, a lawyer, is included on this list because, as of the end of the 2007 reporting period, he was challenging an incumbent — namely seven-term Republican Rep. John Shadegg , whose 59 percent vote share in 2006 was the low water mark of his House career in a Phoenix-based district he had typically dominated. But Lord, as of the next FEC filings in mid-April, will find himself competing for a space on a different top 10 list: candidates seeking open House seats. That’s because Shadegg stunned the political communities in both Arizona and Washington, D.C., by announcing last Monday that he is retiring from Congress at the end of this term. While the Republican Party is expected to try to recruit a strong candidate to defend the seat, Lord has a head start as the choice of his own party’s leadership — the Arizona Democratic Party cut him a $5,000 check on Dec. 31 — and hasn’t needed to spent much of his receipts because he will be unopposed or will face meager opposition in the Sept. 2 primary election.

7) Mark Schauer, Democrat, Michigan’s 7th ($501,000). Schauer, a state senator, is challenging freshman Republican Rep. Tim Walberg in a district that takes in Battle Creek, Jackson and other territory in south-central Michigan. Schauer has raised more than the incumbent since the beginning of 2007 ($577,000 vs. $562,000), and his cash total also exceeds Walberg’s $438,000. It’s very rare for a challenger to out-raise an incumbent.

8) Charlie Brown, Democrat, California’s 4th ($483,000) Brown, a retired Air Force lieutenant colonel, is in the same position as sixth-ranked Arizona Democrat Lord: This will be his final appearance on the incumbent-challenger list, because he is now campaigning for an open seat. Brown had planned on a rematch campaign against nine-term Republican Rep. John T. Doolittle , who — burdened by ethics controversies — won by just 3 percentage points in 2006 in a district that usually leans strongly Republican. But Doolittle, whose persistent ethics problems put him at even greater risk of losing the seat in 2008, announced in January that he will retire rather than wage a re-election campaign. It remains to be seen whether Brown can continue the aggressive fundraising pace with Doolittle out of the race. The Republican candidates are former Rep. Doug Ose, who held the neighboring 3rd District seat from 1999 to 2005, and former state Sen. Rico Oller, who lost a 2004 primary bid to succeed Ose in the 3rd.

9) Judy Feder, Democrat, Virginia’s 10th ($483,000). Feder, a Georgetown University professor and former dean who has a deep background in health care policy, also is a rematch candidate. She’s back for a second try in 2008 against veteran Republican Rep. Frank Wolf, who won their 2006 race by 57 percent to 41 percent. That was Wolf’s lowest winning percentage since 1982, and district precincts in northern Virginia are trending more Democratic than Republican these days. But unseating Wolf will again be a very difficult challenge for Feder.

10) Dean Andal, Republican, California’s 11th ($471,000). Andal, a former member of the California Assembly and the state Board of Equalization, is taking on freshman Democratic Rep. Jerry McNerney , who defeated Republican Rep. Richard W. Pombo in 2006.