A 12-year Republican lock on Congress came to an abrupt end in 2006, as voters punished U.S. President George W. Bush for the quagmire in Iraq.

Democrats rode the U.S. leader's perceived mishandling of Iraq to take control of both the Senate and the House of Representatives from Bush's Republican party in elections held last month.

A Democrat-controlled Congress, which takes power next month, is expected to make the president's last two years in the White House tough ones, ending the virtual rubber stamp Bush has enjoyed since coming into office in January 2001.

During the six years of the Bush era so far, Democrats have had little impact on his policies, only able to raise questions in limited hearings and non-binding resolutions.

But Democrats are expected to press the U.S. president heavily to reverse key policies, leaving Bush few of the tools that allowed him to snub the opposition.

As soon as November's votes were counted, Democrats boosted pressure on the president to set a timetable for pulling U.S. troops out of Iraq and to engage directly with Syria and Iran on bringing security to Iraq.

A week before the election Bush had been defiant, saying in a campaign speech that "The Democrat approach in Iraq comes down to this: The terrorists win and America loses."

But just hours after the Republican defeat, which even Bush acknowledged was a trouncing, the president bowed to pressure and replaced Secretary of Defense Donald Rumsfeld, the embattled architect of the U.S. invasion and occupation of Iraq.

Bush's party also lost when Democrats successfully painted them as fostering a "culture of corruption" in Washington.

The epithet stuck with voters who had seen the previous two years full-up with scandals involving lobbyists, under-age congressional aides, numerous Republican lawmakers and millions of dollars in questionable contracting deals, campaign donations and skewed legislation.

One scandal saw the top Republican in the House of Representatives, Tom Delay, forced to give up his seat. Another saw the conviction of arguably the most powerful Republican lobbyist in Washington, Jack Abramoff.

Republicans were also embarrassed five weeks before the election when another senior representative had to resign his seat on charges that he had made sexual overtures to numerous teenage male aides in Congress.

Democrats charged as well that Florida representative Mark Foley's behavior had been known for years to Republican leaders but that they had covered it up.

The case was like a gift from heaven for Democrats, who had stood by for years as Republicans parroted anti-homosexual stances to curry the most conservative voters.

But even as Democrats enjoyed, with heady anticipation, the prospect of finally coming to power, the fragility of their control of Congress was underscored this month when a U.S. senator was rushed to the hospital after suffering a brain hemmorhage.

Lawmakers of both parties will be watching to see how Senator Tim Johnson fares during what is expected to be a lenghthy convalescence, since Democrats' precarious one-vote majority in the Senate means that with the loss of even one seat, the 100-member body would revert to Republican control.

Democrats are challenged even if they hold on to Johnson's seat. Bush can use his veto power to reject their proposals, and their weak majority in the Senate -- 51 seats to the Republicans' 49 -- will make it difficult to override a veto.

Excepting minor bills and procedural laws, they will find it hard to reverse the major Bush initiatives of the past five years or to push through ambitious programs the Republicans don't back.

Moreover, Bush still controls military and foreign policy, making it difficult for the Democrats to force a withdrawal of troops from Iraq.

Democrats have encountered other setbacks as well. Representative Nancy Pelosi, who in January becomes the first woman ever to preside over the House as speaker, was rebuffed in her choice for top lieutenant. Democrats instead voted one of her party rivals in as majority leader.

Still, control of Congress gives Democrats a platform to begin fighting to recover the presidency in 2008.

Two top Democratic contenders, U.S. senators Hillary Clinton and Barack Obama, are already clearing the field of rivals for the nomination, in what could turn out to be a thrilling head to head showdown.

Meanwhile, with Bush unable to stand for reelection and his vice president Dick Cheney saying he is not interested in the top White House job, U.S. Senator John McCain is the early favorite to win the Republican nomination, although pundits also have their eyes on former New York City mayor Rudolph Giulliani and former Massachusetts governor Mitt Romney.