Since he arrived in Washington in January 2017, President Donald Trump has taken American politics for a white-knuckled joy ride.

His bombast, his lies, his vows, his hirings and firings have rattled a city used to protocol and tradition.

But this week another phase of his presidency begins. Mr Trump will have to deal with a US House that is controlled by representatives of the Democratic Party.

No longer can he expect that his legislative demands will be met by a single-party Congress. Republicans still control the US Senate, but the balance of power is now shifting away from them and Mr Trump.

To understand the significance, a quick civics lesson. Each of the 50 US states has two senators, but the House seats are divided by population. The largest states, like California, Texas and New York, have dozens of representatives.

But seven states — Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont and Wyoming — have a single representative. The rest lie in between.

For legislation to pass the US Congress, it must be approved by both Houses, in a form that is acceptable to each. However, the House has some unique powers that in themselves can block much of what Mr Trump wants to do legislatively in the second half of his term.

Shutdown more urgent than impeachment

Much has been said about the power of the House to impeach the president, a severe rebuke that has only been handed out twice in US history. The first impeachment was of Andrew Johnson in 1868; the second of Bill Clinton in 1999.

Despite the Watergate crisis, Richard Nixon was not impeached; he resigned before impeachment proceedings could begin.

Neither Johnson nor Clinton were removed from office, which required a trial in the Senate.

While there is support among some opponents of Mr Trump for impeachment hearings, Democratic Representative Nancy Pelosi, who is set to become House Speaker for a second time, does not consider it a priority.

"I don't think there's any impeachment unless it's bipartisan," she said in November.

Instead, Ms Pelosi has a more immediate task on her hands: restarting the US government.

Since December 22, federal agencies have been closed, except for the most essential services.

Workers have either been furloughed, or asked to work without pay.

The shutdown took place when Mr Trump refused to accept a deal without $5 billion in funding for the wall he wants built along the US-Mexico border.

Sorry, this video has expired Border patrol clash with migrants

A 'Trump shutdown'

Ms Pelosi and Senate Democratic Leader Charles Schumer of New York have laid responsibility for the impasse at Mr Trump's feet, calling it a "Trump shutdown." Mr Trump, meanwhile, has rained blame on the Democrats via Twitter.

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But Ms Pelosi has a key card to play. The House must approve funding for federal activities, such as the wall. And she has vowed to introduce a spending bill immediately upon the House's return that would open the government again.

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That won't end the suspense, however. Any bill from the House Democrats would have to be approved by the Senate, and then signed by Mr Trump, who at this stage does not want to be the one to blink over a core promise of his campaign.

Senate Republican leaders say they don't want to bring up the bill without assurances that Mr Trump will sign it.

And the President, it has been said repeatedly, does not consider any negotiation ever to be completed, even when a bargain has been reached.

So, despite the arrival of the Democratic House, Washington could simply be at a standstill in the near future. That does not mean things will be calm, however.

Sorry, this video has expired Trump says shutdown "will hopefully not last too long"

Mueller haunts Trump presidency

Special prosecutor Robert Mueller's investigation of Russian interference in the 2016 election looms over the entire situation, like the ghosts in Charles Dickens's A Christmas Carol.

Thus far, his probe has resulted in 192 criminal charges, 36 indictments or guilty pleas, and a prison sentence, according to Axios, and the investigation keeps inching close to Mr Trump and his family members.

On Sunday, Mr Trump's ire at the investigation was joined by that of his attorney, the former New York City mayor Rudolph Giuliani.

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Once, Mr Giuliani was the US attorney for the Southern District of New York, prosecuting the kind of big-name figures that Mr Trump was at the time. So it's remarkable to see him challenge Mr Mueller in this fashion.

For his part, Mr Mueller is neither seen nor heard, unlike the politicians his investigation will greatly affect.

Ms Pelosi, who took a Hawaiian vacation before returning to Washington, does not have the luxury of staying silent, if she is to effectively lead the newly powerful Democrats. And Mr Trump has shown he can neither be quiet or truthful.

The Washington Post reported that he lied an average of 15 times daily during 2018.

But to play off a movie and song title, the Dems are back in town. And the action is about to get interesting.

Micheline Maynard is an author and journalist who writes regularly about American politics.