Republicans have recaptured control of the U.S. Senate and expanded their edge in the House of Representatives, giving them a majority in both houses of Congress for the final two years of President Barack Obama's presidency.
Democrats held 55 of the Senate's 100 seats before Tuesday's midterm elections, but Republicans gained at least seven seats with wins in Arkansas, Colorado, Iowa, Montana, North Carolina, South Dakota and West Virginia.
Results were not yet final in three other Senate races early Wednesday.
A third of the Senate was up for reelection Tuesday, including the Kentucky seat held by Senate Republican Mitch McConnell from Kentucky. He earned a sixth term in office and will become Senate majority leader in January.
McConnell told supporters that the election was not about him or his Democratic opponent, Alison Lundergan Grimes.
"It was about a government that people no longer trust to carry out its most basic duties: to keep them safe, to protect the border, to provide dignified and quality care for our veterans," McConnell said, adding the government was "too busy focusing on things it shouldn't be focused on at all."
Meanwhile, Republicans added at least nine seats in the House, where they already had a large majority.
In Colorado's Senate race, incumbent Democratic Mark Udall was defeated by Republican challenger Cory Gardner. "Tonight we shook up the Senate. You shook up the Senate," Gardner told supporters. "We go to work to fix a Washington that is out of step, out of touch and out of time."
A pledge to rein in the federal government helped propel Republican Senate candidate Joni Ernst to victory in Iowa. She said it was about “getting [federal] spending under control, keeping taxes low, and cutting red tape so businesses can grow and invest.”
Tuesday was not a clean sweep for Republicans, as Democrats held onto Senate seats in states such as New Hampshire, where Jeanne Shaheen won another term in office.
"I will work with anyone in the Senate – Democrat, Republican, Independent – to get things done," she said.
And in Louisiana, incumbent Democratic Senator Mary Landrieu will face Republican Bill Cassidy in a December runoff, since neither won a majority of the votes.
Landrieu challenged her rival to a series of debates on issues including education, jobs and the economy, "Social Security and Medicare, health care, energy and the environment and, yes, international affairs and trade."
Obama's agenda faces challenge
McConnell told supporters he hopes to work with Obama, a Democrat, despite ideological differences.
"I do not expect the president to wake up tomorrow and view the world any differently than he did this morning. He knows I will not, either," McConnell said. "But we do have an obligation to work together on issues where we can agree."
House Speaker John Boehner said the Republican-controlled Congress will work on energy and jobs legislation, which he said Senate Democrats have been stalling while in control. "It's time for government to start getting results," he said.
With control of Congress, Republicans could raise new disputes with Obama over his signature legislative achievement, health care reform, which has allowed millions of people to secure insurance coverage they could not previously afford. Many Republicans view the law as excessive government involvement, and have repeatedly called for its repeal.
Republicans also have attacked Obama's handling of the Ebola crisis and called for approval of an oil pipeline from Canada through the central U.S., and a curb on government regulation of businesses.
Some opposition lawmakers have disputed the president's handling of Russia's intervention in Ukraine and U.S. airstrikes against Islamic State militants in Iraq and Syria.
The United States' two main political parties also are feuding over spending and tax policies and immigration reform.
Obama had vowed to set new immigration rules by executive order by the end of the year, after the House balked at acting on comprehensive reforms approved by the Senate. Some Republicans already are saying they will seek to block the president from unilaterally changing the country's immigration policies to allow millions of migrants who entered illegally to stay in the United States.
Troubled by political gridlock
Many voters said they are disgusted with political gridlock between Democrats and Republicans in Washington.
"They have to start doing something," Arizona voter Lee Deremo said of congressional politicians, "and I think it just needs to change, plain and simple."
Anger with Washington played heavily in the elections, according to Republican strategist Ford O’Connell: "Two-thirds of America thought the country was going in the wrong direction. They wanted a change in direction. And now it is up to Republicans to bring that change."
Tuesday’s vote was a referendum on Obama’s leadership, according to American University professor Allan Lichtman.
"President Obama dragged down the Democrats," the political historian said via Skype. "It is not as if Republicans in this election represented grand ideas, inspiring solutions to national problems. They were simply pinning every Democrat [candidate] to an unpopular Democratic president."
Reacting to a new political reality in Washington, Obama has invited congressional leaders of both houses and both political parties to the White House Friday.
VOA's Michael Bowman contributed to this report.
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