There is no longer much pretence at measured debate or a determined pursuit of bipartisan solutions. Instead, the United States is gripped by a daily onslaught of shocking revelations, bitter recriminations and denials that seem unlikely ever to end.

The partial government shutdown is now the longest in history, but Republican strategist Andy Surabian told the New York Times this was just the beginning of a “non-stop political war” that will last until the end of the Trump presidency — if not beyond.

Mr Trump on Monday confirmed he had rejected Republican Senator Lindsey Graham’s suggestion he reopen the government while negotiations continue, while placing the blame on Democrats for the ongoing impasse.

“We have drugs, we have criminals, we have gangs, and the Democrats don’t want to do anything about it,” he told reporters at the White House. “The Democrats are stopping us, and they’re stopping a lot of great people from getting paid.”

Nine of 15 cabinet departments are closed, along with important agencies including NASA and the Food and Drug Administration. Air travel, farming subsidies and national parks have all been affected and 800,000 federal workers are on leave without pay or working without pay.

‘I NEVER WORKED FOR RUSSIA’

But this was not even Mr Trump’s biggest problem over the weekend, after the Times sensationally revealed the FBI opened a counterintelligence investigation into whether the US President had been influenced by Russia when he fired FBI director James Comey in 2017.

Special Counsel Robert Mueller then picked up some of this in his investigation into alleged Russia collusion by Mr Trump’s campaign team during the 2016 presidential election.

The Washington Post, meanwhile, revealed Mr Trump repeatedly withheld details of his conversations with Vladimir Putin, even removing an interpreter’s notes after the leaders’ Helsinki summit in July.

The Finland discussion was remarkable because Mr Trump questioned his own intelligence agencies’ conclusion Russia sought to influence the 2016 election — not the first time he caused concern in the US by taking Mr Putin’s view.

“I never worked for Russia,” Mr Trump told reporters as he left the White House for a New Orleans farmers convention on Monday. “Not only did I never work for Russia, I think it’s a disgrace that you even asked that question because it’s a whole big fat hoax.”

It’s believed to be the first time a US president has denied being a “foreign agent”.

“Never in history has an American president been required to answer such serious, credible questions about his loyalties,” Michael D’Antonio, author of the book Never Enough: Donald Trump and the Pursuit of Success wrote for CNN.

Mr Trump also attacked the FBI officials behind the investigation as “ known scoundrels” and “dirty cops.”

It was a clearer denial of the allegations, after some White House aides were reportedly troubled by his failure to decisively rule out the possibility on Fox News this weekend.

“I’m going to ask you, are you now or have you ever worked for Russia, Mr President?” asked host Jeanine Pirro.

Mr Trump replied: “I think it’s the most insulting thing I’ve ever been asked. And if you read the article, you’d see that they found absolutely nothing.”

He also addressed the Post’s story on him covering up discussions with Mr Putin. “We were talking about Israel and securing Israel and lots of other things, and it was a great conversation,” he said. “I’m not keeping anything under wraps. I couldn’t care less.”

‘I DON’T TRUST THE FBI AS FAR AS I THROW THEM’

House Intelligence Committee chairman Adam Schiff suggested it was time Republicans supported Democrats in trying to subpoena Mr Trump’s interpreter.

“The American people need to know the President is working in our national interest, and for no other end,” he said.

Another Democrat, Senator Richard Durbin, asked on the US ABC’s This Week: “Why is he so chummy with Vladimir Putin, this man who is a former KGB agent, never been a friend to the United States, invaded our allies, threatens us around the world and tries his damnedest to undermine our elections?

“Why is this President Trump’s best buddy? I don’t get it.”

But House Minority leader Kevin McCarthy told CBS’s Face the Nation that the President “likes to create a personal relationship, build that relationship, even rebuild that relationship, like he does with other world leaders around.”

Secretary of State Mike Pompeo told the show any notion the President was a threat to American security was “absolutely ludicrous.”

Trump supporter Mr Graham turned the spotlight back on the FBI, saying there should be checks within the bureau to prevent such an investigation. “I find it astonishing, and to me, it tells me a lot about the people running the FBI,” he said. “I don’t trust them as far as I throw them.”

THE CONFLICT CONTINUES

In tandem with the President’s escalating retaliation to a constant stream of scandals, the Democrats have become increasingly stubborn in their positions.

They are determined to help Mr Mueller complete his Russia investigation and report to Congress. They have been setting up more investigations into Mr Trump’s business interests, taxes, campaign and administration since taking the majority in the House of Representatives this month. The first articles of impeachment have been filed.

House Foreign Affairs Committee chair Eliot Engel plans to replace a subcommittee on terrorism with one investigating Mr Trump’s foreign policy.

House Speaker Nancy Pelosi made it clear she will not be the one to back down in the shutdown stand-off, with Democrats only willing to provide $US1.3 billion ($A1.8 billion) for border security.

This fierce battle over Mr Trump’s demand for $US5.7 billion ($A8 billion) looks set to be just the first in a stream of wars over policy, budgeting and every aspect of American life.

As predicted before Christmas, this is a Congress utterly divided, and with few qualms about publicising the squabbling, treachery and dissent that characterises this government.

The most common question among Washington insiders is now: how will history look back at this strange and fraught time?

The fighting will only ramp up this week, as the shutdown continues to inflict pain on ordinary citizens, not least the government workers who cannot pay their bills.

On Tuesday, Democrats will question former Attorney General William Barr, Mr Trump’s nominee to step back into the role, about the Mueller investigation.

Last year, Mr Barr wrote a memo criticising the probe — a fact that is particularly concerning for Democrats with Deputy Attorney General Rod Rosenstein set to depart after overseeing the investigation. But he says he will see the investigation through, with his prepared testimony reading: “On my watch, Bob will be allowed to complete his work.”

Senate minority leader Chuck Schumer also intends to force a vote in the Senate this week on White House plans to lift sanctions on Russian oligarch and Putin associate Oleg Deripaska’s businesses.

Mr Trump’s former campaign chairman Paul Manafort is one of at least 14 Trump associates who interacted with Russians during the campaign and transition. New details emerged last week, including the fact Mr Manafort shared polling data with Konstantin Kilimnik, an associate who allegedly has ties to Russian intelligence

There were also allegations a Russia-friendly Ukrainian peace plan could have had personal benefits for Mr Manafort.