The big gains House Democrats made in the past two election cycles largely resulted from “spreading the playing field,” jargon for the party’s efforts to compete for seats that in years past it essentially ceded to the Republicans. Now as Republicans try to rebound in the 2010 elections, they are trying their own version of this strategy by testing some entrenched Democratic incumbents — such as Tennessee’s Bart Gordon and John Tanner .

The emergence of active GOP challengers to these long-entrenched members has prompted CQ Politics to change its ratings from Safe Democratic to Likely Democratic both in the 6th District, represented by Gordon for 13 terms, and the 8th, Tanner’s congressional base for 11 terms.

The Likely rating means the incumbents still are heavily favored to win re-election, but the Republicans at least have some chance of making one or both races competitive.

The fact that the Republicans have lined up anyone at all for these contests is an achievement in itself. Tanner was unopposed in 2008, while Gordon had no Republican Party challenger and won with 74 percent of the vote over an independent candidate.

Both have prospered over the years by projecting images as center-right Democrats even though their heavily conservative districts tend to favor Republican candidates for other major offices. In 2008, Republican presidential nominee John McCain trounced Democrat Barack Obama by 62 percent to 37 percent in Gordon’s mid-Tennessee district, which includes the city of Murfreesboro and some fast-growing Nashville suburbs, and carried the vote by 56 percent to 43 percent in Tanner’s west Tennessee district, which includes Jackson and suburbs of Memphis.

Republicans have long argued they could compete on this turf if they could drum up strong candidates. And they think they finally have solid contenders in Stephen Fincher, a farmer and gospel singer who has signed on to tackle Tanner in the 8th District, and Lou Ann Zelenik, chairwoman of the Rutherford County Republican Party, who is challenging Gordon in the 6th District.

Fincher came out of nowhere to report $303,000 in fundraising receipts as of Sept. 30, all from individuals. Since Fincher’s unexpected showing, the National Republican Congressional Committee (NRCC) — the House GOP’s campaign arm — has touted him as a candidate with strong grass-roots support in western Tennessee, largely because of his family singing group’s popularity. The NRCC recently added Fincher to its “Young Guns” program for promising candidate recruits and cited McCain’s strong district showing as a key indicator that Fincher is viable.

Compared to Fincher’s number, Tanner’s $62,000 in third-quarter receipts seems tepid. But fundraising is less urgent for the veteran incumbent, who has been piling up a big cash reserve through a series of easy re-election campaigns. Tanner was sitting on about $1.4 million in cash on hand at the end of September. He also has never been seriously challenged in a House general election: The 62 percent in his first race, back in 1988, remains his career low, and 2008 marked the third time in 11 tries that he ran unopposed.

Gordon, who first won a House seat in 1984, was once seen as vulnerable by Republican strategists because he was a protege of Texas Democrat Jim Wright, (1955-89), who served as House Speaker from 1987 to 1989 but resigned after House Republicans — led by conservative firebrand Newt Gingrich, R-Ga. (1979-99) — pilloried him over a questionable book deal. Gordon had one near-defeat experience, hanging on with 51 percent in 1994, a terrible year for the Democrats nationally and in Tennessee.

Gordon has since settled in comfortably and has not slipped below 62 percent since 1998. He was tapped as chairman of the House Science and Technology Committee in 2007, and he reported about $1.3 million in the bank as of Sept. 30.

But the 6th District has a pronounced conservative lean, and it is one of the few districts in the nation where McCain won bigger as the 2008 Republican presidential nominee (a 25 percentage-point margin) than President George W. Bush did in 2004 (a 20-point margin).

And Gordon, since the Democrats claimed a House majority in the 2006 elections, has been voting more of a party line than was typical in the past. A Congressional Quarterly study showed he voted with most House Democrats against most Republicans on mainly party-line votes 90 percent of the time in the 110th Congress (2007-08), a jump from 74 percent during the Republican-controlled 109th Congress (2005-06). He hit a 95 percent party unity score during the first half year of the current 111th Congress.

Zelenik and her Republican allies think Gordon is handing them issues to use against him. They have already pointed to his support of a House energy bill, aimed at containing global warming, that includes provisions to “cap and trade” industrial emissions that Republicans reject as economically burdensome, and his vote earlier this year to move health care legislation, also strongly opposed by the GOP, out of the Energy and Commerce Committee.