Harry Reid, the Democratic leader in the Senate, says FBI director James Comey may have broken the law by revealing the bureau was investigating emails possibly linked to Hillary Clinton.
He accused James Comey of violating an act which bars officials from influencing an election.
News of the FBI inquiry comes less than two weeks before the Election Day.
The FBI has meanwhile obtained a warrant to search a cache of emails belonging to Huma Abedin, a top Hillary Clinton aide.
Emails from Huma Abedin are believed to have been found on the laptop of her estranged husband, former congressman Anthony Weiner.
There are reportedly 650,000 emails to search through, making it unlikely investigators can give a verdict on them before election day.
The FBI believes the emails might be “pertinent” to its previous inquiry into Hillary Clinton’s use of a private server when she was secretary of state in the Obama administration.
The case was closed in July without any charges being brought against Hillary Clinton.
Anthony Weiner is subject to a separate investigation on suspicion of sending explicit messages to an underage girl.
Harry Reid accused James Comey of practicing double standards with the intention of helping one political party over another.
In a letter, Harry Reid said James Comey may have violated the Hatch Act, which bars officials from using their position to influence an election.
“Through your partisan actions, you may have broken the law,” he said.
Harry Reid also accused James Comey of withholding “explosive information about close ties between [Republican candidate] Donald Trump, his top advisers, and the Russian government”.
“The public has a right to know about this information. I wrote to you months ago calling for this information to be released to the public,” Harry Reid said.
Richard Painter, a professor at the University of Minnesota Law School and the chief White House ethics lawyer from 2005 to 2007, revealed on October 30 he had filed a complaint against the FBI with the Office of Special Counsel, which investigates Hatch Act violations.
Writing in the New York Times he said: “I never thought that the FBI could be dragged into a political circus surrounding one of its investigations. Until this week.”
Opinion polls showed Hillary Clinton’s lead against Donald Trump tightening even before the email controversy surfaced again.
An ABC News/Washington Post poll published on October 30 put Hillary Clinton just one percentage point ahead.
Hillary Clinton has described James Comey’s actions as “unprecedented” and “deeply troubling”.
However, Donald Trump has praised the FBI’s decision, accusing the Department of Justice of protecting Hillary Clinton in a “rigged system”.
“The Department of Justice is trying their hardest to protect the criminal activity of Hillary Clinton,” Donald Trump told a rally in Nevada.
It emerged on October 30 that the Department of Justice had urged the FBI not to inform Congress of the new inquiry so close to the election.
The Republicans have won control of the Senate in the midterm elections, increasing their power in the final two years of Barack Obama’s presidency.
The party won in Arkansas, Colorado, Iowa, Montana, North Carolina, South Dakota and West Virginia.
It is expected to post more gains as votes are counted in other states.
Republican Senator Mitch McConnell, poised to lead the chamber, said the result was a vote against “a government that people can no longer trust”.
In the midterms, so-called because they fell half way into Barack Obama’s second four-year term in office, about one-third of the Senate, the entire House of Representatives, 36 of 50 state governors, and countless state and local offices were up for election.
Throughout the campaign, Republicans focused on voter dissatisfaction with Barack Obama, a Democrat, describing the vote as a referendum on his presidency.
As the first results came in late on November 4, it became clear they had made convincing gains in the chamber.
With the votes still being counted in many states, the Republican Party easily won the six seats it needed to win control of the Senate.
The party controls 52 seats, and is tipped to win more.
The Republicans have won control of the Senate in the midterm elections, increasing their power in the final two years of Barack Obama’s presidency
When the new Congress is sworn in January, it will mark the first time the Republicans have held both chambers since 2006.
They will now have the power to complicate, if not block completely, Barack Obama’s agenda in the last two years of his tenure in the White House.
Control of the Senate will also enable the Republicans to stymie his ability to name new federal judges, cabinet members and senior government officials.
In addition to seats the party won from the Democrats, the Republicans retained seats in Alabama, Georgia, Idaho, Kansas, Kentucky, Maine, Mississippi, Nebraska, Oklahoma, South Carolina, Tennessee, and Texas.
In Louisiana, neither of the top two candidates gained 50% of the vote, forcing a run-off election in early December.
In Virginia, Democrat Mark Warner was expected to retain his Senate seat amid a much tighter than expected race with Republican ex-lobbyist Ed Gillespie.
One of the night’s key early results came in Kentucky, where Mitch McConnell, the Republican Senate minority leader, fended off Democrat Alison Lundergan Grimes.
Mitch McConnell will now become the Senate majority leader, giving him control over the chamber’s legislative agenda and floor proceedings.
“It wasn’t about me or my opponent,” he told supporters as he declared victory, “it was about a government that people can no longer trust.”
Current Senate Majority Leader Harry Reid congratulated Mitch McConnell in a short statement.
“The message from voters is clear: they want us to work together,” said Harry Reid of Nevada, whose role in the soon-to-be Democratic minority remains uncertain.
“I look forward to working with Senator McConnell to get things done for the middle class.”
As well as taking the Senate, the Republicans are projected to increase their majority in the House of Representatives, where all 435 members were up for re-election.
They also made gains among the 36 governorships up for re-election.
Republican governors survived tough re-election battles in Florida, Maine and Wisconsin.
In two results that illustrate the breadth of the Republican sweep, the party’s candidates won in Maryland and Massachusetts, two of the most Democratic-friendly states in the nation. Republican Bruce Rauner also won in Illinois – Barack Obama’s home state – against incumbent Democratic Governor Pat Quinn.
Political gridlock in Congress has already reached historic levels and was a major concern among voters, with many expressing their frustration with the lack of progress on the key issues facing the nation.
Analysts say the Republicans’ victory could make the situation even worse before the president poll in 2016.
Republican leaders have already pledged to move forward on their key policy priorities, pressing Barack Obama to negotiate on their terms
“It’s time for government to start getting results and implementing solutions to the challenges facing our country, starting with our still-struggling economy,” said Republican House Speaker John Boehner.
The US shutdown negotiations have been shifted to the Senate.
The Democratic and Republican leaders in the Senate held direct talks for the first time in weeks, but there is little sign of any breakthrough, correspondents say.
The shutdown began when Congress missed the October 1st deadline to pass a budget.
The US faces another deadline on Thursday to raise its debt limit.
If a deal is not reached by then, the US faces potential default, a prospect which has caused alarm both domestically and abroad.
Senator Dick Durbin, a Democrat, said the aim was to reach a deal on extending the debt limit before markets reopen on Monday.
The talks between Senate Majority Leader Harry Reid and Senate Republican leader Mitch McConnell earlier on Saturday represented the first face-to-face meeting between the two since July, the New York Times reported.
“The conversations were extremely cordial but very preliminary of course – nothing conclusive, but I hope that our talking is some solace to the American people and to the world,” said Harry Reid.
The US shutdown negotiations have been shifted to the Senate
“We had a good meeting,” said Mitch McConnell, without elaborating.
Harry Reid then went to the White House for talks with President Barack Obama.
But he rejected a plan put forward by Republican Senator Susan Collins to allow the government to increase its debt limit until January 31st, 2014.
Democrats have a majority in the Senate, but could not muster enough support to advance a proposal to lift the debt ceiling there.
Talks between House Republicans and the White House had collapsed earlier.
Republicans have refused to pass a new budget unless President Barack Obama agrees to delay or eliminate the funding of the healthcare reform law of 2010.
Hundreds of thousands of federal employees have been sent home as a result of the shutdown.
The White House has repeatedly said it would not undermine the law, known as Obamacare, nor negotiate over larger budget matters, until Republicans vote to end the threat of default.
It has also rejected a short-term deal over the debt limit.
“It wouldn’t be wise, as some suggest, to just kick the debt ceiling can down the road for a couple of months, and flirt with a first-ever intentional default right in the middle of the holiday shopping season,” President Barack Obama said.
Shares in New York are trading lower as the prospect of a shutdown of some US government activities looks increasingly likely.
The Dow Jones and S&P 500 both fell 1% shortly after the open, but then recovered some lost ground.
The deadlock also unsettled European stock markets, already nervous about the political crisis in Italy.
The US needs to agree a new spending bill before the financial year ends at midnight on Monday.
But political divisions have resulted in a stalemate and there are worries over the economic impact of a shutdown of the US government.
If the government does shut down on October 1, as many as a third of its 2.1 million employees are expected to stop work – with no guarantee of back pay once the deadlock is resolved.
National parks and Washington’s Smithsonian museums would close, pension and veterans’ benefit cheques would be delayed, and visa and passport applications would be stymied.
Programmes deemed essential, such as air traffic control and food inspections, would continue.
Shares in New York are trading lower as the prospect of a shutdown of some US government activities looks increasingly likely
Investors will be keen to know if Friday’s job report will be released.
The monthly non-farm payrolls report is one of the most closely watched pieces of US economic data.
Employees at the Labor Department’s Bureau of Labor Statistics (BLS), who prepare the report, would be among those who would stood down in the event of a shutdown.
“All survey and other program operations will cease and the public website will not be updated,” said Erica Groshen, commissioner of the BLS, said in a memo published on the department’s website.
Republicans are targeting President Barack Obama’s healthcare law, popularly known as Obamacare.
Early on Sunday, the Republican-run House of Representatives passed an amended version of the Senate spending bill that removed funding for the healthcare law.
US Senate Majority leader Harry Reid has vowed that his Democrat-led chamber will reject the Republican bill.
“Tomorrow, the Senate will do exactly what we said we would do and reject these measures,” said Adam Jentleson, a spokesman for Senate Majority Leader Harry Reid.
“At that point, Republicans will be faced with the same choice they have always faced: put the Senate’s clean funding bill on the floor and let it pass with bipartisan votes, or force a Republican government shutdown.”
Speaking for the president, White House spokesman Jay Carney said: “Any member of the Republican Party who votes for this bill is voting for a shutdown.”
The president, he said, would also veto the Republican bill.