A rising sense of dread stalked the US Republican Party on Wednesday, after Democrats snatched a rock solid conservative congressional seat, in their third upset pick-up in a row.

The victory in the southern state of Mississippi was the latest sign that President George W. Bush's party could face a Democratic rout in November's congressional elections, party as a result of the unpopularity of his policies.

"It was another wake-up call," said John Boehner, leader of the Republican minority in the House of Representatives, as Democrats celebrated the win in one of the most conservative bastions in the country.

Republican lawmakers had grim faces as they trudged out of a caucus meeting here, even as their leaders pledged later in the day to relaunch their congressional agenda, under the slogan "The Change You Deserve."

Tom Cole, who heads Republican congressional campaign efforts, delivered an unusually stark warning, telling his party's candidates "to take stock of their campaigns and position themselves for challenging campaigns this fall."

Democratic House majority leader Steny Hoyer, promised Tuesday's victory by Travis Childers pointed to a devastating election year for Republicans, who lost control of both the House and Senate in 2006.

"We believe it is a harbinger of things to come in November," Hoyer said, who mocked the "The Change You Deserve" slogan, saying it had already been used to market an anti-depressant medicine.

Democrats are looking to expand their 37 seat majority in the House, and increase their tally in the 100 seat Senate from the current 51, towards a filibuster proof majority of 60.

Republicans are particularly bracing for losses in the Senate, as in what was already shaping up as a bad year, they have 23 seats up for reelection compared to only 12 for the Democrats.

Democrats are seizing on a Washington Post/ABC News poll this week that found that eight in ten Americans believe their country is heading in the wrong direction and that Democrats are more favored to fix the problems.

Hoping that Bush's deep unpopularity will hit his party in November, some Democrats have visions of a sharp political realignment, with expanded House and Senate majorities, and a Democrat back in the White House.

But Roy Blunt, the number two Republican in the House said Wednesday that the result in Mississippi did not necessarily augur a Republican meltdown in November, saying that Childers ran on a conservative platform, and had not embraced Democratic presidential front-runner Barack Obama.

"You had the winning candidate saying repeatedly that he didn't know Nancy Pelosi or Barack Obama.

"You had him talking about cutting taxes, having less spending, being pro-gun and pro-life (anti-abortion)," Blunt said.

Childers beat Republican rival Greg Davis in Mississippi's first congressional district, which voted overwhelmingly for Bush in 2004, by 54 percent to 46 percent.

The result was also encouraging for Obama, who went down to his own big loss to Hillary Clinton in Tuesday's Democratic primary in West Virginia.

Republican campaigns have been trying to tie candidates in Democratic congressional races to the Illinois senator, betting that framing him as a liberal will depress the vote in deeply conservative districts.

But Democrats have now won recent elections in Mississippi, Illinois and Louisiana, despite the attacks.