Leading Democrat Nancy Pelosi has refused to rule out Donald Trump being either indicted or impeached while in office, warning the president will face a “different world” thanks to a new Congress.

Ms Pelosi is set to become speaker of the House of Representatives as the Democrats take over the majority in that chamber and described the topic of a potential presidential indictment as an “open discussion”.

The senior Democrat said it is possible that special counsel Robert Mueller could seek an indictment against the sitting president, despite Justice Department guidelines against such action. Mr Mueller is leading the federal investigation into Russian election meddling in the 2016 presidential election, possible collusion between Moscow and Trump campaign officials which has been inching closer to the White House in recent months.

“I do not think that that is conclusive,” Ms Pelosi told NBC’s Today show about the Justice Department guidance. “I think that that is an open discussion. I think that is an open discussion in terms of the law,” she added.

Mr Trump has denied any wrongdoing and has repeatedly called the Mueller inquiry a “witch hunt”.

As for impeachment – something that a number of prominent Democrat supporters have called for – Ms Pelosi said that while she believed such action would not benefit the country, she would not dismiss it either.

“We have to wait and see what happens with the Mueller report,” Ms Pelsoi said. ”We shouldn’t be impeaching for a political reason, and we shouldn’t avoid impeachment for a political reason. So we’ll just have to see how it comes”.

Whatever happens in terms of indictment or impeachment, Ms Pelosi said that Mr Trump should expect much more oversight of his administration now that Democrats will control one chamber of Congress.

Who could be running against Trump in 2020? Show all 23 1 /23 Who could be running against Trump in 2020? Who could be running against Trump in 2020? Joe Biden The former vice president - poised to be a frontrunner - has announced his run. He recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well AFP/Getty Who could be running against Trump in 2020? Bernie Sanders The 2016 runner-up has announced that he will be running again in 2020 Getty Who could be running against Trump in 2020? Hillary Clinton The 2016 Democratic presidential candidate and former Secretary of State says she is “still considering” whether she will run again. Getty Who could be running against Trump in 2020? Pete Buttigieg The Indiana mayor and war veteran will be running for president. If elected, he would be the first openly LGBT+ president in American history. Getty Who could be running against Trump in 2020? Kamala Harris The former California attorney general will be running for president in 2020. Introduced to the national stage during Jeff Sessions’ testimony, she has endorsed Medicare-for-all and proposed a major tax-credit for the middle class. AP Who could be running against Trump in 2020? Elizabeth Warren The Massachusetts Senator has formally launched her bid for president in 2020. A progressive Democrat, she is a major supporter of regulating Wall Street. AP Who could be running against Trump in 2020? Beto O’Rourke The former Texas congressman told Oprah Winfrey that he “has been thinking about running for presidency”, but stopped short of formally announcing his bid to run in 2020. AFP/Getty Who could be running against Trump in 2020? Wayne Messam Mayor of the city of Miramar in the Miami metropolitan area, Wayne Messam has announced his bid. He intends to run on a progressive platform against the "broken" federal government. He favours gun regulations and was a signatory to a letter from some 400 mayors condemning President Trump's withdrawal from the Paris Climate Accord. Vice News Who could be running against Trump in 2020? Kirsten Gillibrand The New York Senator formally announced her presidential bid in January, saying that “healthcare should be a right, not a privilege.” Getty Who could be running against Trump in 2020? Cory Booker The New Jersey Senator has announced that he will be running for the presidency in 2020. If he secures the nomination he said finding a female vice president would be a priority. Getty Who could be running against Trump in 2020? John Delaney The Maryland congressman was the first to launch his bid for presidency, making the announcement in 2017. AP Who could be running against Trump in 2020? Julian Castro The former San Antonio mayor announced his candidacy in January and said that his running has a “special meaning” for the Latino community in the US. Getty Who could be running against Trump in 2020? Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but is likely to face tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad. Getty Who could be running against Trump in 2020? Andrew Yang The entrepreneur has announced his presidential candidacy, and has pledged that he would introduce a universal basic income of $1,000 a month to every American over the age of 18. AFP/Getty Who could be running against Trump in 2020? Marianne Williamson The author and spiritual advisor has announced her intention to run for president. She had previously run for congress as an independent in 2014 but was unsuccessful. Getty Who could be running against Trump in 2020? John Kerry The former secretary of state has said he is still thinking about whether to run. Getty Who could be running against Trump in 2020? Michael Bloomberg The entrepreneur and former New York mayor– with a net worth of around $50bn – has said he will decide by the end of February whether to seek the presidency. AFP Who could be running against Trump in 2020? Howard Schultz Former Starbucks CEO Howard Schultz has not yet ruled out running for president in 2020, despite criticism that his bid could help re-elect Mr Trump by dividing the Democrat vote. AP Who could be running against Trump in 2020? Eric Holder The former attorney general has said he will decide in “the next month or so” whether to run as a 2020 presidential candidate. AP Who could be running against Trump in 2020? Eric Swalwell The California congressman said he is “ready to do this” and will decide before April whether to run. MSNBC Who could be running against Trump in 2020? Terry McAuliffe The former Virginia governor, who worked to elect Democratic governors during 2018 midterms, said there was a “50 per cent” chance he would run. AP Who could be running against Trump in 2020? Sherrod Brown The Ohio senator is still undecided about whether to run for president in 2020. Who could be running against Trump in 2020? Mitch Landrieu The former New Orleans mayor said he doesn’t think he will run for president, but “never say never”. AP Photo/Jacquelyn Martin

Speaking to USA Today as part of a number of interviews ahead of the swearing-in of the new Congress, Ms Pelosi said this “different world” will come as shock to the president.

“He was used to serving with a Republican Congress, House and Senate that was a rubber stamp to him. That won’t be the case,” Ms Pelosi said. “Oversight of government by the Congress is our responsibility.”

Ms Pelosi and other Democrats have laid out a host of areas where they intend to conduct oversight or investigations. In the last few weeks top Democrats have said they plan to look into the president’s finances, his daughter Ivanka’s use of private email and his foreign policy decisions.

On the topic of impeachment, Ms Pelosi told USA Today that she would not seek to seek grounds for the move unless it’s “clearly bipartisan” and has Republican support.

The biggest issue for Congress to deal with is the partial government shutdown which has lasted nearly two weeks. It started on 22 December after Democrats refused to sanction $5bn in specific funding for a wall on the US-Mexico border that was one of his major campaign promises.

Democrats have offered $1.3bn in general border security funding, and will likely push through two separate spending bills to re-open the government through the House on Thursday. However, with Republicans having control of the Senate and Mr Trump also having to sign any legislation, there is a stalemate.

Mr Trump has blamed Democrats for the shutdown, with his latest tweets claiming it is related to the 2020 presidential election, which the president says Democrats “can’t win against him”.

However, Ms Pelosi has laid the blame for the stoppage at the door of the White House.

“This is the Trump shutdown, through and through. That’s why he has proudly taken, in his view, proudly taken ownership of it. There’s no escaping that for him,” Ms Pelosi told NBC. “That doesn’t mean we take any joy in the fact that there is a Trump shutdown. We want government to open.”

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Straight after a remarkable televised stand-off with Mr Trump in the Oval Office over the budget ahead of the shutdown, Ms Pelosi met with House Democrats and reportedly dismissed Mr Trump’s wall as “a manhood thing”.