With President Bush planning high-profile initiatives in his second term like Social Security (search) reform, Democrat leaders are digging in, vowing to stop the Bush agenda dead in its tracks.

"We, as Democrats, have got to stand up and fight aggressively from day one," said outgoing national party chairman Terry McAuliffe, who has been asked by some Democratic lawmakers to retain his position as head of the Democratic National Committee (search).

Hoping to re-energize a party demoralized by Sen. John Kerry's defeat in the 2004 presidential election, Democrats plan confrontation, McAuliffe said.

"We disagree with George Bush. Fifty-six million people came out and voted for John Kerry to defeat George Bush. Those 56 million people are counting on those Democrats to get in there and fight for them," he said.

Even the centrist Democratic Leadership Council (search), which prefers bipartisan results over gridlock, backs a stonewall strategy. Co-founder Will Marshall told FOX News that Democrats distrust the president and are unlikely to budge on major initiatives, particularly Social Security.

"Many Democrats are very skeptical about entering into any kind of negotiation with President Bush on Social Security, which, after all, is the crown jewel of Democratic programs," Marshall said.

Democrats complain that it could cost $2 trillion to reform Social Security to include the president's voluntary private accounts. Furthermore, they argue, it will lead either to a reduction in benefits or an increase in premiums or both.

The DNC, which is electing a new party chairman in February, is spoiling for a fight with the president. The Democrats' pick next month for McAuliffe's successor could signal the party's long-term ideological direction.

Former presidential candidate Howard Dean (search), who emerged as a champion of the angry left last year, officially jumped into the race Tuesday. He made clear that his priorities are likely to clash with Bush's.

"The Democratic Party will not win elections or build a lasting majority solely by changing its rhetoric, nor will we win by adopting the other side's positions. We must say what we mean and mean real change when we say it," he wrote in a statement on his Web site announcing his candidacy.

Dean is running against former Indiana Rep. Tim Roemer (search), a moderate who opposes abortion and who many Democrats say could better court centrist swing voters. Also in the race are former Texas Rep. Martin Frost, who was a member of the Democratic leadership with a reputation for hard-nosed anti-GOP partisanship; and Simon Rosenberg, who until recently was chairman of the moderate New Democrat Network (search). A handful of lesser-known candidates are also in the race.

Because the DNC is made up largely of liberal activists, insiders say Dean may have an edge for chairman. Democratic Party officials told FOX News, however, that they have been warned that if Dean becomes chairman, some conservative Democrats will bolt the party, striking a blow against the minority party that it perhaps can't afford to suffer.

Click in the video box near the top of the story to watch a report by FOX News' Carl Cameron.