Democrats took another Republican-held U.S. House seat in a special election Saturday, suggesting that the party remains on track for significant expansion of its congressional majorities in 2008.

Louisiana Democrat Don Cazayoux, a young moderate with state legislative experience, snatched a seat that Republicans had held since the 1970s by a 49-46 margin over a well-funded campaign by veteran Republican legislator Woody Jenkins.

The win extends the Democratic majority in the House to 235-198 and it continues a pattern of special-election wins for the party in seats that have traditionally been thought of as Republican strongholds — including the Illinois turf of former House Speaker Dennis Hastert.

But it does something far more significant.

Republicans and their allied special-interest groups had sought to save the seat by “nationalizing” — or, to be more precise, racializing — the contest with a campaign that sought to tie Cazayoux to Democratic presidential frontrunner Barack Obama. Hoping to capitalize on concerns about Obama’s former minister, the Rev. Jeremiah Wright, in order to exploit racial divisions in the south and other regions of recent Republican strength, GOP operatives have developed advertising schemes that feature images of Obama, Wright and local Democratic candidates.

The strategy was implemented in Louisiana and is also being used in an upcoming Mississippi special election.

The Louisiana results had Maryland Congressman Chris Van Hollen, the able chair of the Democratic Congressional Campaign Committee, declaring, “Republicans were reminded that ‘all politics is local.’ House Republicans tried to nationalize this election, illegally coordinated with Freedom’s Watch, used false and deceptive special interest smears, and funneled nearly a million dollars into a district that Republicans held for more than three decades.”

But don’t expect the Republicans, who have struggled to come up with a plan to divert voter attention from economic and foreign-policy concerns, to abandon plans to exploit racial divisions in upcoming contests.

Cazayoux was an attractive candidate with deep Louisiana roots, while Jenkins was a controversial figure even in Republican circles — in no small part because of his past ties to former Ku Klux Klansman David Duke. And still the final result was a close one.

That has encouraged National Republican Congressional Committee, which argued that the anti-Obama campaigning helped Jenkins make up “substantial ground” in the closing days of the contest.

“This election speaks to the potential toxicity of an Obama candidacy and the possible drag he could have down-ballot this fall,” argued the NRCC team in a memo that, despite its sore-loser tone, makes clear the intention of the Republican party to make the fall campaign one very long, and very ugly, “Willie Horton” ad.