Donald Trump has warned the new Democratic majority in the House of Representatives that he will retaliate if they investigate him.

The US president said in a White House press conference held the day after the US midterm elections: “Investigate me, and I’ll investigate you — and the government will grind to a halt.”

Noting that his Republican Party retained control of the upper chamber of the US Congress, he said that if Democrats in the House come after him “we’ve got a thing called the US Senate”.

US Senate elections 2018.
(PA Graphics)
US House of Representatives elections
(PA Graphics)

Mr Trump, who was both combative and conciliatory at different times during the press conference, said Democrats and Republicans should set aside partisanship to work together.

Some House Democrats have threatened to use the subpoena power they will gain in January to investigate Mr Trump and administration actions. But the president warned that he will respond in kind and the government will suffer.

He also said that the Democrats have “nothing, zero” on him.

Of the special counsel’s Russia investigation that has shadowed his administration for more than 18 months, Mr Trump said that he could end it now but lets it continue.

Mr Trump’s remarks on party dynamics came after Senate majority leader Mitch McConnell said he had spoken with House Democratic leader Nancy Pelosi about how they might “find a way forward” in a divided Congress next year.

Mr McConnell said the Republicans “had a very good day” despite the House loss.

He said: “I’m proud of what happened. The president was very helpful to us.”

Mr McConnell added that he and Ms Pelosi are “not unfamiliar” with one another as long-time leaders and colleagues.

On congressional action for the rest of the year, he said he could not imagine taking up immigration and acknowledged that the Democratic House and Republican Senate were likely to go their separate ways when it comes to the legislative agenda.

“Areas for legislative agreement will be more limited,” he said.

“The one issue that leader Pelosi and I discussed this morning where there could be a possible bipartisan agreement would be something on infrastructure, but there could be a lot of other things.”

Mr McConnell said that Democrats in the House will have to decide how much they want to “harass” Mr Trump.

That echoed a similar message from Mr Trump, who on Twitter cautioned Democrats not to use their new House majority to launch investigations into his administration.

He tweeted: “If the Democrats think they are going to waste Taxpayer Money investigating us at the House level, then we will likewise be forced to consider investigating them for all of the leaks of Classified Information, and much else, at the Senate level. Two can play that game!”

Mr McConnell said the contentious, partisan fight over US Supreme Court Justice Brett Kavanaugh’s nomination was “very helpful” in winning Senate seats, like an “adrenaline shot” for Republican voters.

Mr Kavanaugh was confirmed last month after a California professor accused him of sexual assault when both were teenagers.