Montana's Republican Senate seat shifted into the Democratic column Wednesday afternoon, giving the party control of 50 seats and leaving Virginia as the lone roadblock to a Democratic sweep or a Republican split of Congress.

Democratic challenger John Tester claimed victory in Montana, besting three-term Republican incumbent Sen. Conrad Burns.

In Virginia, the State Board of Elections announced it would not certify the outcome of the race between incumbent Republican Sen. George Allen and Democratic challenger Jim Webb until Nov. 27, after which recounts could begin. There are no automatic recounts in Virginia. The candidates were separated by about 7,800 votes out of more than 2.3 million cast, with indications from both camps that any final outcome could wind up in court.

The Associated Press projected Webb as the winner late Wednesday, which would give Democrats complete domination of Capitol Hill for the first time since 1994, but the race is still too close for FOX News to call.

However, sources close to Allen told FOX News on Wednesday evening that the incumbent doesn't intend to "drag this out," and that he could concede as early as Thursday afternoon.

Republican and Democrat party officials dispatched lawyers to Virginia to observe vote counting, as well as to canvass votes counted on Election Day.

"No one is more interested in the outcome of this race than we at the Allen camp," said the Republican's adviser Ed Gillespie, who added that election officials are looking over their numbers for "mathematical mistakes, tabulation errors, juxtaposition of numbers" and other human error.

"The conclusion of the canvass will be the final official results," Gillespie said.

"I know the counting will continue through the night, it will continue tomorrow," Allen told supporters Tuesday night.

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The too-close-to-call race didn't deter Webb, who bounded on stage just after 1 a.m. Wednesday to thank his supporters for a hard-fought victory.

"The votes are in and we won," Webb told a crowd of jubilant supporters at a northern Virginia hotel ballroom. "This is a great moment for all of us who believe in an inclusive society ... I will look forward to representing all of you to the best of my ability."

Allen's campaign had no comment, and FOX News, along with other major news outlets considered the race a virtual dead heat.

With the Montana vote decided, Democrats succeeded in shifting five Senate seats to their side of the aisle. A change of six seats into the Democratic aisle is needed to take the Senate out of Republican hands.

Democrats already were basking in the glow of victory Wednesday, fresh off capturing control of the U.S. House of Representatives, and in convincing fashion.

Democrats needed to swing 15 seats to take control, but by the end of the day they had won 26 seats.

Despite the "thumpin" Bush said Republicans took in the House and the possibility of also losing control of the Senate, President Bush on Wednesday vowed to reach out to Democrats to show the American people that things can get done, no matter the makeup of the legislative and executive branch.

"As the head of the Republican Party, I share a large part of the responsibility," Bush told reporters at the White House.

"I told my party's leaders that it is now our duty to put the elections behind us and work together with the Democrats and independents on the great issues facing this country," he continued, saying he called Democratic leader Nancy Pelosi, the putative speaker of the House, early Wednesday morning to congratulate her on her party's gains and to voice his desire to working with Democrats to find "common ground."

"As the majority party in the House of Representatives, they recognize that in their new role they now have greater responsibilities," he said, joking that his first act of bipartisan outreach since the election was sharing with Pelosi the names of some Republican interior decorators.

For her part, Pelosi promised that "Democrats intend to lead the most honest, the most open and the most ethical Congress in history."

Senate Democratic Leader Harry Reid of Nevada said Americans "have come to the conclusion, as we did some time ago, that a one-party town simply doesn't work."

Other phone calls Bush made Wednesday were to Reid and Senate Minority Whip Dick Durbin, of Illinois, House Minority Whip Congressman Steny Hoyer, D-Md., and Democratic Congressional Campaign Committee Chair Rahm Emanuel, D-Ill. He said their party did a "superb job" of turning out their votes. Both Reid and Durbin were invited to the White House on Friday for a coffee meeting.

"I congratulated them on running a strong campaign in the Senate. And I told them that, regardless of the final outcome, we can work together over the next two years," Bush said.

The White House described all the phones call with Democrats as a nature of "goodwill."

The president invited Democratic leaders to come to the White House in the coming days to talk about the agenda for next year. Pelosi and Hoyer were invited to join the president for lunch at the White House on Thursday so they can "start to strategize on how to work together."

Three GOP incumbents lost in Indiana, three more in Pennsylvania, two in New Hampshire, one in North Carolina, one in Kansas, one in California and more elsewhere. Democrats won open seats, which were held by Republicans, in New York, Ohio, Florida, Arizona, Colorado, Wisconsin, Iowa and Texas.

The Senate, however, proved to be a tougher mountain to climb.

In Missouri, Democrat Claire McCaskill had to wait until after 1 a.m. Wednesday to claim victory in a close race against incumbent Republican Jim Talent .

"All of our efforts fell a little bit short this time, but they were worth the making," said Talent, who was embroiled in a bitter debate about a proposed state amendment backing embryonic stem cell research.

Elsewhere, Republican Bob Corker defeated Democratic Rep. Harold Ford Jr., in the race for the Tennessee Senate seat being vacated by outgoing Senate Majority Leader Bill Frist.

In Pennsylvania, incumbent Republican Rick Santorum lost his seat to challenger Bob Casey . Republicans also lost a Senate seat in Ohio, when incumbent Sen. Mike DeWine was beaten by Democratic Rep. Sherrod Brown .

In Rhode Island, longtime Republican Sen. Lincoln Chafee lost to Democratic challenger Sheldon Whitehouse.

Dems: America Wants 'Change'

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"It's a great night for Democrats, it's a great night for America," Sen. Charles Schumer , head of the Democratic Senatorial Campaign Committee, told supporters at the Hyatt in Washington around midnight Tuesday as Democrats celebrated their wins. "We will tell you and all of America, not only can we do better, but we will do better."

Pelosi is set to become the first female speaker of the House. Hoyer of Maryland announced he will run for the majority leader post, the second in command in the House.

Bush also called House Speaker Dennis Hastert , who survived a surprisingly tough battle, and thanked him for running a tough campaign, assuring the embattled Illinois Republican that "we will all work together."

Hastert later said he had no intention of running for the House minority leadership post. He is preoccupied with the Mark Foley congressional page scandal, and questions about what he knew of Foley's electronic messages to under-age male pages.

White House spokesman Tony Snow said Bush is "obviously disappointed" that the House changed hands, but pointed out that the president believes "the challenges haven't changed. Democrats have the responsibility to help the president win the war, and to keep the economy growing."

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In the Senate, meanwhile, speculation grew regarding Sen. Joe Lieberman 's loyalty in spite of the long-time Democrats declaration Monday to FOX News that if elected as an Independent he would caucus with Democrats. Lieberman beat Democrat Ned Lamont on Tuesday night, just three months after losing to the wealthy businessman in the Democratic primary. After that loss, Lieberman announced he would run as an independent in Tuesday's election.

"Dear friends, this year's campaign, to say the obvious, was a long journey on which you — my dear supporters — and I were tested as never before but we never wavered in our beliefs or in our purpose, did we? And we never gave up, did we?" Lieberman asked supporters Tuesday night, thanking the labor groups and firefighters who made up a large portion of his base.

"And tonight, tonight, thanks to the voters of Connecticut, our journey has ended in victory and hope and the opportunity to make a difference for six more years," added Lieberman, who was shunned by fellow Democrats, including New York Sen. Hillary Clinton, a potential 2008 presidential contender.

In Maryland, Democratic Rep. Ben Cardin held off Republican Lt. Gov. Michael Steele for the seat vacated by retiring Sen. Paul Sarbanes. The race was called early for Cardin, but Steele refused to concede in spite of trailing by more than 152,000 votes, until Thursday morning.

Wiping away tears as he addressed reporters in Annapolis Thursday, Steele said he congratulated Cardin for his win and then urged him to keep his promises to bring changes to Congress.

Steele said he told Cardin, "Don't forget the poor."

"It's one thing to talk about change. It's something very different to do it," Steele said.

Cardin stressed his opposition to the war throughout his campaign and blasted Steele for not renouncing the war. "It's clear that Americans want a different course in Iraq," Cardin said.

In New Jersey, Democratic incumbent Sen. Bob Menendez beat Republican state Sen. Tom Kean Jr., son of the popular former governor and Sept. 11 commission chairman who shares his name.

Rep. Bernie Sanders easily captured the Senate seat in Vermont to keep it independent after the retirement of Sen. James Jeffords. Sens. Robert Byrd of West Virginia and Ted Kennedy of Massachusetts both went on to win record-breaking ninth terms.

Just after leaving the White House Tuesday night, Snow pointed out that a number of so-called Blue Dog (conservative) Democrats were elected, saying that provides some "interesting opportunities." Snow said Bush will continue to push for "comprehensive immigration reform," among other issues.

FOX News' Bret Baier, Carl Cameron, Liza Porteus and The Associated Press contributed to this report.