In an increasingly conservative America, Democrats are seeking to compete electorally by shifting left and abandoning officeholders who appeal to middle-of-the-road independents and even conservatives.

Democrats aren't just hoping to take back Congress this year; they also are trying to rid the party of so-called "right-wing Democrats."

Rep. Henry Cuellar represents the solidly Democratic 28th district in Texas. Yet activists from his party are backing his primary challenger, former Rep. Ciro Rodriguez.

"People have been able to get a good picture of Henry Cuellar's record," Mr. Rodriguez told The Washington Times. "He doesn't stand with working families. On issues like tax cuts, the estate tax and immigration, he has voted with Republicans down the line."

Mr. Cuellar has been endorsed by the conservative Club for Growth, a group that typically endorses Republicans and has supported primary challengers to centrist Republicans such as Sen. Arlen Specter of Pennsylvania. The Club for Growth estimates it has raised $150,000 for Mr. Cuellar's campaign.

After a contentious Democratic primary battle in 2004, Mr. Cuellar defeated Mr. Rodriguez, a three-term incumbent, by a mere 58 votes. Since then, Mr. Cuellar has angered many liberals with his support for the war in Iraq and other Republican-backed policies.

Mr. Rodriguez acknowledges that centrists have a place in the Democratic Party, just not in his district. "This is not a swing district. Voters here deserve someone who will represent their values," he said.

The 28th District, stretching from the Rio Grande to San Antonio, is 70 percent Hispanic. In the 2004 general election, Mr. Cuellar received 59 percent of the vote against Republican opponent James Hopson.

Mr. Rodriguez said Democratic activists have pumped more than $250,000 into his campaign in the weeks since his primary challenge gained national attention. "Thank God for it," he said.

Liberal groups such as MoveOn.org and Democracy for America (DFA), as well as leading liberal bloggers and unions such as the AFL-CIO and the Service Employees International Union, are backing Mr. Rodriguez.

Mr. Rodriguez "is a real Democrat," said DFA Chairman Jim Dean. "He is not a shill for the White House. We've raised about $40,000 for Ciro so far. It's been a pretty good response, especially considering a lot of people didn't even know about this race until a few weeks ago."

A significant part of Mr. Rodriguez's opposition to Mr. Cuellar stems from their differences on trade. Mr. Cuellar was a vocal proponent of the Central American Free Trade Agreement (CAFTA), which Mr. Rodriguez opposes.

Cuellar campaign spokesman Colin Strother said free trade and conservative values are popular in the 28th district.

"Ten of the 11 counties in our district have experienced growth since [the North American Free Trade Agreement] was passed," Mr. Strother said. "Ciro's most vocal supporters are not in the district. Our district is Catholic, Hispanic and conservative. Ciro doesn't represent those values."

Charles Mahtesian, editor of Almanac of American Politics, said the March 7 Democratic primary contest will be as bitter as it was two years ago.

"It's the stated policy of the party to support incumbents," Mr. Mahtesian said. "But at least in Washington and in Congress there are a lot of people secretly hoping it turns out differently."

Speaking as a Republican, I wholeheartedly support this strategy, which seems to me to be the political equivalent of treating a shaving cut by slitting your throat. The 28th District will never vote for a Republican – unless the Democrats abandon the base of conservative Hispanic Catholics. That is where this strategy is headed.