President Donald Trump and his Department of Justice are taking a combative stance towards Democrats after their victories in the midterm elections, signalling intense conflict ahead as lawmakers prepare aggressive investigations into the executive branch next year.

Trump set the tone on social media, describing investigative requests already made by Democrats as extortion at the highest level and saying they should be held accountable. Attorney General Todd Blanche echoed the president and said criminal investigations of Democrats are possible. Blanche, who previously served as Trump's personal defence lawyer, also suggested he may use his power as head of the Justice Department to blunt congressional inquiries.

Speaking on the Sunday news shows, Blanche said Democrats were not allowed to go around threatening members of the administration or companies, and that Trump was extremely worried about that, rightly so. Blanche was interviewed on Fox News Sunday and CNN's State of the Union.

Democrats promise investigations, not intimidation

Representative Robert Garcia, who is poised to chair the powerful House Oversight Committee in the next Congress, is preparing investigations into what he calls the Trump crime family. Garcia, a California Democrat, said Democrats were not going to be intimidated, adding that the days of not fighting back were over. He was speaking on CNN, where he rejected Blanche's warning and said his party would not be intimidated however it was pursued.

Democrats take control of both chambers of Congress in January, and they have made clear that impeachment is an option. House Democratic leader Hakeem Jeffries of New York said that if people had been shortchanging, screwing over or stealing from the American people, they needed to be held accountable in a manner consistent with Congress's constitutional role.

The early rhetoric sets up a showdown that is likely to define Trump's remaining two years in office and test the power of Congress to check the White House. About seven in ten voters nationally say Congress is not doing enough to provide checks and balances on the presidency, according to the AP Voter Poll, a survey of more than 100,000 midterm voters.

Some Democrats warn against overreach

The planned investigative onslaught is also a source of tension inside the Democratic Party, with many warning that delivering on the central promise to voters, action to lower the cost of living, must take precedence. Some fear their resounding wins, which gave them healthy majorities in the House and Senate, will prove fleeting if conflict with Trump defines the agenda.

Senator-elect Adam Hamilton, the first Democrat elected to the chamber from Kansas in 94 years, expressed scepticism about impeachment, saying his campaign was about trying to bring people together and that he did not want the next two years spent dividing the country further. He said he was not as interested in impeachment as in setting up guardrails, while accepting that some investigations were necessary. Senator Bernie Sanders, a Vermont independent who caucuses with Democrats, said he wanted to hold Trump accountable but warned Democrats could not spend all their time investigating Trump and had to stand up for working-class families.

Miller appointment and Hegseth resolution

Jeffries, who is on the cusp of becoming the nation's first Black House speaker, said he would be ready to work across the aisle whenever and wherever possible to deliver real results. But on Sunday he criticised Trump's choice of longtime adviser Stephen Miller to succeed Susie Wiles as chief of staff, calling him an awful choice and casting doubt on working with him. Nationally, about six in ten voters said the administration's actions on immigration enforcement had gone too far, according to the AP Voter Poll.

Jeffries also said he supports a pending resolution from Representative Thomas Massie, a Kentucky Republican, to impeach Defence Secretary Pete Hegseth, and that Democrats would discuss it when they returned to the Capitol this week. Jeffries said Hegseth had got to go and described himself as a hard yes on the resolution. Hegseth dismissed the push in a video as all about the politics of personal destruction, saying it would not work with him.

At least two incoming Democratic senators also expressed reservations on Sunday about Democratic leader Chuck Schumer, who is expected to be re-elected to his post after leading his party back to the majority. Hamilton said he had told Schumer, who is running unopposed, that he meant no disrespect but that the New Yorker was a polarising figure in Kansas, and that he was looking for a leader who could lead from the centre and unite rather than divide. Senator-elect Abdul El-Sayed of Michigan said he had been committed to Senator Chris Van Hollen, but acknowledged the Maryland Democrat did not appear to be running for the post.