House Democrats have generally shown strong unity over the six months since the party took control of Congress, based on their gains in the 2006 elections.

While the public’s attention so far has been focused on the highly divisive congressional debates over hot-button issues such as the Iraq war and immigration, House Democrats have encouraged party discipline by largely sticking to issues that, polls show, are generally popular with the electorate. Most Americans, for example, supported an increase in the minimum wage that House Democrats unanimously backed in January.

But, as is always the case, there are members who break with their Democratic leaders and colleagues more often than most — with longtime Mississippi Rep. Gene Taylor the leading party dissident, breaking with the Democratic position on nearly a third of House votes that fell mainly along partisan lines.

Of the 10 Democrats registering the lowest party unity scores so far this year, six — including Taylor — are from the strongly conservative-leaning South, while another is from the Republican stronghold of Utah.

Nine of the 10 represent districts that President George W. Bush carried for the Republican Party in 2004, in some cases by wide margins. The one exception is Georgia’s 12th District, but even there, Democrat John Kerry edged Bush by just six-tenths of 1 percentage point — the same margin by which Democratic Rep. John Barrow staved off defeat in his 2006 win for a second House term.

While Taylor’s strongly conservative brand of Democratic politics has kept him safe in southern Mississippi’s Republican-leaning 4th District for nearly 18 years, five of the 10 lowest party unity scores were recorded by members who took over Republican-held districts just last year in the big Democratic upsurge.

These and other victorious Democrats portrayed Republican incumbents as “rubber stamps” for Bush and House Republican leaders. They are thus endeavoring to present themselves as independent-minded voices as they enter their first re-election contests in their politically competitive, if not Republican-leaning, districts.

But Republicans surely will claim that these Democrats still vote far too frequently with the positions of House Speaker Nancy Pelosi, a California liberal.

The analysis is based on CQPolitics.com’s latest study of House “party unity” scores during the current 110th Congress. Party unity, one of Congressional Quarterly’s signature vote analyses, measures how often a lawmaker sides with members of his or her own party against most members of the other party on mainly party-line votes.

The following is a roundup of the Democratic members with the lowest party unity scores, with summaries of their political situations back home. This is followed by capsule descriptions of members with slightly higher party unity numbers, all of whom took over Republican seats in the last election and could face serious challenges next year.

1. Gene Taylor, Mississippi’s 4th District (69.2 percent). Long one of the most conservative House Democrats, Taylor has dominated his heavily conservative district in southern Mississippi — a territory that the Republicans have not seriously contested in years.

2 (tie). Heath Shuler, North Carolina’s 11th (73.8 percent). Shuler has the most contrarian record among House Democratic freshmen. Democratic strategists will not mind this, given that he last year defeated eight-term Republican Rep. Charles H. Taylor in a strongly conservative western North Carolina district.

2 (tie). John Barrow, Georgia’s 12th (73.8 percent). Barrow was re-elected by just 864 votes last year over Republican challenger Max Burns, a former one-term congressman whom Barrow defeated in 2004. The 12th District’s lines were altered, and the Democratic margin in the district reduced, in a mid-decade redistricting crafted by the Republican-controlled state legislature between the 2004 and 2006 elections.

4. Jim Marshall, Georgia’s 8th (74.0 percent). Like Barrow, Marshall also narrowly avoided defeat in 2006 in a redistricting-altered district. Unlike Barrow, Marshall represents a strongly conservative-leaning district and already has a serious opponent for 2008: Rick Goddard, a retired Air Force Major General.

5. Jim Matheson, Utah’s 2nd (75.1 percent). Matheson’s district gave Bush two-thirds of its votes in the 2004 presidential election, though the 22 percentage- point victory margin for center-right Democrat Matheson in 2006 will complicate Republican recruitment efforts.

6. Jason Altmire, Pennsylvania’s 4th (75.7 percent). Altmire was an upset winner in 2006 over three-term Republican Rep. Melissa A. Hart, who has not ruled out a comeback attempt in 2008 in a district that includes suburbs of Pittsburgh and which is socially conservative and economically populist.

Also considering a House bid is Lynn Swann, the former Pittsburgh Steelers football great who was the Republican nominee for governor last year: Though Democratic Gov. Edward G. Rendell won an overall landslide, Swann finished narrowly ahead in the 4th District.

Ron Francis, a former county commissioner, already is running for the Republican nomination.

7. Joe Donnelly, Indiana’s 2nd (75.8 percent). Donnelly, a social-issues conservative, defeated two-term Republican Rep. Chris Chocola in a north-central Indiana district that includes South Bend and part of Kokomo. Republican Luke Puckett has filed paperwork with the Federal Election Commission to prepare a 2008 campaign.

8. Dan Boren, Oklahoma’s 2nd (76.2 percent). Boren — a son of David L. Boren, a former Oklahoma governor and senator — dominated in his two elections in Oklahoma’s “Little Dixie” district, which is conservative-leaning but ancestrally very Democratic.

9. Brad Ellsworth, Indiana’s 8th (77.3 percent). Ellsworth, who trounced Republican Rep. John Hostettler in 2006, represents a southwestern Indiana district that is strongly conservative-leaning: Of the 39 House Democrats who were first elected in 2006 — three former members also won last year — Ellsworth represents a district that backed Bush in 2004 more strongly than any other (with 62 percent of the vote).

So far, though, no Republican candidate has filed to challenge Ellsworth, who has bucked Democratic leaders by taking conservative stands on embryonic stem cell research.

10. Nick Lampson, Texas’ 22nd (78.6 percent). Lampson’s 79 percent party unity score is lower than any score he amassed during his previous House tenure (1997 through 2004), when he represented a district that was Democratic-leaning. His scores during his past House tour ranged from 82 percent to 88 percent.

The political leanings of Texas’ 22nd, which takes in suburbs of Houston and part of the city, guarantee a difficult re-election campaign for Lampson — who was elected in 2006 to succeed Republican Tom DeLay, the resigned former House majority leader.

Lampson has gotten some early breaks for 2008, though: Several Republicans who had been considering a run — including Sugar Land Mayor David Wallace, long considered a prospective House candidate — decided against running.

One confirmed Republican candidate is Shelley Sekula Gibbs, who won a special election last November to fill the remainder of DeLay’s term in the 109th Congress — but on the same day lost a write-in campaign to Lampson for the full term in the 110th.

Other Notable House Democrats

11. Christopher Carney, Pennsylvania’s 10th (81.4 percent). Carney has one of the more Republican-leaning districts among first-term Democrats, and was greatly aided in 2006 by the fact that Republican incumbent Don Sherwood was badly damaged by a sex scandal. There is a long list of potential GOP candidates, though Democrats took note recently that the Republican field will not include U.S. Attorney Thomas A. Marino — a top prospect who recently said that he will not challenge Carney.

12. Melissa Bean, Illinois’ 8th (81.8 percent). Bean narrowly defeated investment banker David McSweeney to win a second term last year in a historically Republican-leaning district that takes in suburbs northwest of Chicago.

Bean in May was one of 13 House Democrats who voted against a party-crafted budget resolution.

13. Zack Space, Ohio’s 18th (83.0 percent). Space last year was easily elected to succeed Republican Bob Ney, who resigned shortly before the election and after his guilty plea to federal corruption charges in a case involving disgraced lobbyist Jack Abramoff. The 18th District, which takes in rural expanses of eastern and southern Ohio, voted decisively for Bush in the 2004 presidential election, but Democrats since then have made inroads throughout the state.

At least four Republicans have filed paperwork with the FEC to challenge Space, though none is well-known.

14. Patrick Murphy, Pennsylvania’s 8th (83.2 percent). Murphy, an Iraq war veteran who ousted one-term Republican Rep. Michael G. Fitzpatrick in 2006, has been a vocal party loyalist in promoting a redeployment of U.S. troops from that conflict. He is somewhat less party-line on economic policy. His district, which is dominated by suburban Bucks County north of Philadelphia, is trending more Democratic than Republican.

18. Harry E. Mitchell, Arizona’s 5th (84.3 percent). Mitchell, who unseated six-term Republican J.D. Hayworth in 2006, also has occasionally broken with Democratic leaders on some budget votes. This is not surprising, given that his district, which includes Scottdale and Tempe, has the highest median income of any Arizona congressional district.

22. Tim Mahoney, Florida’s 16th (84.7 percent). Mahoney last year narrowly defeated Joe Negron — the Republican running in the stead of Rep. Mark Foley, who had resigned shortly before the election after reports of his improper communications with underage House pages forced him to resign in disgrace. Several Republicans have already entered the 2008 race in the 16th, which includes Port St. Lucie and has a generic Republican lean.

27. Gabrielle Giffords, Arizona’s 8th (86.8 percent). Giffords succeeded retiring moderate Republican Rep. Jim Kolbe last year in a politically competitive district that takes in part of Tucson and some of its suburbs. State Senate President Tim Bee has been mentioned as a potential Republican candidate.

28. Baron P. Hill, Indiana’s 9th (86.9 percent). Hill unseated freshman Rep. Mike Sodrel in the 2006 election — their third consecutive matchup, following Hill’s narrow win for a third House term in 2002 and Sodrel’s even closer win over Hill in 2004. While Hill’s 2007 party unity score is among the lowest in his party, he is actually siding with Democratic leaders more frequently than in his first House tenure (1999 through 2004), when his scores ranged from 72 percent to 83 percent.

Sodrel has not ruled out running in 2008, which would set up a highly unusual fourth consecutive matchup in a district that usually votes Republican for president.

29. Nancy Boyda, Kansas’ 2nd (88.0 percent). Boyda in 2006 defeated five-term Rep. Jim Ryun, who beat Boyda in 2004 and who is looking to defeat her again in 2008 — this time as the challenger in a Republican-leaning district that takes in Topeka. Ryun does not have an unimpeded path to a rematch, though, as state Treasurer Lynn Jenkins also is seeking the Republican nomination.

31. Kirsten Gillibrand, New York’s 20th (88.7 percent). Gillibrand last year toppled four-term Republican John Sweeney in an upstate New York district that the GOP had long dominated. Several Republicans have already lined up to challenge Gillibrand in 2008.