(CNN) Donald Trump has a New Year's message for Americans reeling from his disruption and exhausted by his impossible-to-ignore presidency: "CALM DOWN AND ENJOY THE RIDE."

His advice, in one of his first tweets of 2019, suggests there will be no letup in the President's rambunctious behavior in a year that started with him in vintage form, accusing an admired retired general of having a "big, dumb mouth."

A crush of challenges bearing down on the White House, his own sense of liberation after the departures of restraining aides, and the new power dynamics in Washington look set to make the coming year even wilder than 2018.

Trump's ultra-loyal voters, who sent him to Washington to rock establishment elites, are likely to enjoy the pandemonium. For everyone else, it's going to be more difficult in a year that could bring a grave political reckoning.

Trump begins 2019 seeking a face-saving win from a partial government shutdown that's doubling as his first clash with the new Democratic House majority. He invited congressional leaders to the White House on Wednesday for talks as the shutdown stretches into a 12th day.

Before the end of this year, he could be in a fight for his presidency itself, given special counsel Robert Mueller's widening investigation.

Multiple battle fronts

Apart from the shutdown and Mueller, the White House is embroiled in multiple feuds and potential crises, some of them set off by the President's talent for dismantling order. Trump's challenging political situation will test his capacity to impose his will at a time when Washington power is divided after two years of blanket GOP control.

And it will bring immense peril as Democratic committee chairs in the House send volleys of subpoenas to the White House in a campaign of oversight that will come as an unwelcome novelty for Trump.

Trump got a taste of one new source of opposition in changed Washington when Sen.-elect Mitt Romney of Utah wrote a Washington Post op-ed Tuesday declaring that Trump's conduct over the past two years, and particularly over the last month, "is evidence that the president has not risen to the mantle of the office."

But how the 2012 GOP presidential nominee votes, rather than what he writes, will be the true barometer of his willingness to challenge Trump.

The first months of the year will involve crucial deadlines in a tariff duel with China t hat could develop into a major trade war -- or offer Trump a significant victory if he can reach a deal that changes Beijing's economic behavior.

A combative New Year's message b y North Korean leader Kim Jong Un offers the promise of a second summit with Trump or a dangerous deterioration of relations with a power that has yet to honor its commitment to denuclearize.

Trump shocked the Pentagon and lost his defense secretary, James Mattis, with a sudden announcement of a pullout from Syria, though he stepped back slightly by giving the military four months to get out of the war-torn country.

The President's legal liability is growing in the meantime. Every aspect of his political and business life is under investigation, including his 2016 campaign, his transition, his inauguration and his presidency. He was indirectly implicated in directing a campaign finance crime in association with his former lawyer Michael Cohen by prosecutors in New York.

Another potential political vulnerability could emerge if recent stock market volatility is a harbinger of an economic slowdown.

Still, the economy remains the best argument Trump's team can make for the success of his presidency.

"Under President Trump 'unemployment rate is matching its low point of the last half-century,' " the President's spokeswoman Sarah Sanders tweeted on Tuesday, citing a Washington Times article by Stephen Moore, who's a Trump supporter and CNN contributor,

"...An all-time high 130 million Americans now have a job...Wages are rising...Americans are again the most productive & among the highest-paid workers in the world."

Under President Trump "unemployment rate is matching its low point of the last half-century...An all-time high 130 million Americans now have a job...Wages are rising...Americans are again the most productive & among the highest-paid workers in the world" https://t.co/UEAN8TJ8WD — Sarah Sanders (@PressSec) December 31, 2018

The economy is an oasis of stability as 2019 dawns.

Russia's arrest, for instance, of an American, Paul Whelan, on spying charges over the holiday highlights souring relations with Moscow, which could be further tested by the Kremlin's troop buildup along the border with Ukraine.

It would also be no surprise if Trump returns to bashing allied leaders he sees as freeloading off the US defense umbrella while courting strongmen around the globe, a trend in his presidency that emerged again on Tuesday, when he sent congratulations to Brazil's new far-right radical President.

At home, Washington will shortly be consumed by two new confirmation dramas, for Trump's nominee for attorney general, William Barr, and whomever he chooses to succeed Mattis.

The new Democratic House majority will make it tough for Trump to add to his legislative legacy, with presumptive speaker Nancy Pelosi gearing up for showdowns with the President and the Republican-led Senate over health care, campaign finance and voting rights.

Ready for the fight

Facing a year of challenges, Trump is defiant, spoiling for new fights and relishing the opening exchanges of the 2020 presidential race.

The departures of such "adults in the room" as Mattis and chief of staff John Kelly have left the President more liberated to follow his gut than at any previous moment of his term.

By opting to close down parts of the government over his demands for $5 billion in taxpayer cash for a border wall that he had repeatedly said Mexico would pay for, Trump sent a signal about how he would respond to Washington's new reality.

In time, the shutdown may therefore become just the first in a string of dramas engineered by the President to please his political base.

Ultimately, Trump's most loyal supporters could be crucial to his capacity to influence Republican senators, 20 of whom would need to join Democrats to convict him in any Senate impeachment trial.

But the base-appeasing strategy is risky for a President who rarely gets above 45% in opinion polls and who saw his hardline immigration message repudiated in the loss of the House in November.

In the past, government shutdowns have often ended when one party concludes that its political interests are being harmed among swing voters. Trump, however, is not playing on the same field as Democrats, since his decision not to avoid a shutdown was designed to appeal to key conservative commentators and grassroots supporters.

That makes it harder for him to compromise in order to end it.

The President's tactics -- revealed in tweets blasting Democratic leaders as he stayed home alone in the White House over the holidays -- appear to be mystifying even some on his side.

"It's not a question of who wins or loses; nobody's going to win this kind of game. Nobody wins in a shutdown. We all lose, and we look silly," Sen. Richard Shelby, the Alabama Republican who's the chairman of the Senate Appropriations Committee, said Sunday on CBS's "Face the Nation."

Trump, however, seems convinced he is winning the shutdown.

"Border Security and the Wall 'thing' and Shutdown is not where Nancy Pelosi wanted to start her tenure as Speaker! Let's make a deal?" he tweeted on Tuesday.

Border Security and the Wall "thing" and Shutdown is not where Nancy Pelosi wanted to start her tenure as Speaker! Let's make a deal? — Donald J. Trump (@realDonaldTrump) January 1, 2019

But Pelosi sees the chance for some high ground.

"@realdonaldTrump has given Democrats a great opportunity to show how we will govern responsibly & quickly pass our plan to end the irresponsible #TrumpShutdown," the California Democrat wrote Tuesday on Twitter.

.@realDonaldTrump has the Senate, the White House, and the House (for the moment) under Republican control. He has the power to keep government open -- but instead, he says he's going to shut down the government. #TrumpShutdown pic.twitter.com/Pdbo4rH0sG — Nancy Pelosi (@NancyPelosi) December 11, 2018

The dynamic between Trump and Pelosi could be a critical factor in defining the year's political battles. She already has experience as speaker in leveraging a House majority to help prepare the groundwork for a Democratic presidency -- in her tussles with President George W. Bush between 2007 and 2008.

This time around, her task includes keeping a lid on premature impeachment fever, which would help Trump portray Democrats as overreaching in an unreasonable effort to cripple his presidency.

Trump is finding joy in the early combat of the 2020 presidential campaign. It's clear that Democratic contenders must be ready for simultaneous fights -- one with rivals for the nomination and one with Trump.

The President's relish for battle was evident in his voice during a New Year's Eve interview with Fox News hours after Sen. Elizabeth Warren of Massachusetts took her first step toward a campaign.

Asked whether Warren thought she could win the Democratic nomination, Trump returned to the demeaning personal attacks that crushed the GOP field in 2016.