(CNN) The New Year is only a few hours old, but the political forces that are likely to shape a turbulent 2019 are already in play.

President Donald Trump, worried about spurning his most loyal supporters who bonded with him over his 2016 demands for a border wall, is digging deeper into a partial government shutdown that is stretching into an 11th day with no clear way out.

The Democratic presidential race is already firing up following Massachusetts Sen. Elizabeth Warren's announcement in the dying hours of 2018 that she is launching an exploratory committee -- the first step toward a campaign for the party's nomination.

There was an ominous feel to the holidays given the dark cloud hanging over Trump because of special counsel Robert Mueller, whose findings could take the nation down the bitter road to impeachment in the year to come.

But the President doesn't just have to worry about Mueller. Democrats are days away from taking control of the House of Representatives and inaugurating a novel challenge for Trump's presidency -- congressional oversight.

The Dow Jones Industrial Average climbed 265 points to close 2018, in a sleepy session compared to the stomach-churning instability that produced the worst year for stocks in a decade and could fuel economic uncertainty that could play into the 2020 race.

And as always, there are signs of instability and chaos in the White House, with confusion over Trump's exact position on a border wall and his planned Syria troop withdrawal, while key staff vacancies were unfilled.

Shutting government to please the base

Trump stayed at home, often largely alone in the White House over the Christmas and New Year's break, tweeting at Democrats but with no real political movement evident over the shutdown. Often the aim seemed to be to talk solely to his political base -- a trend that is likely to go on all year.

"I'm in the Oval Office. Democrats, come back from vacation now and give us the votes necessary for Border Security, including the wall. You voted yes in 2006 and 2013. One more yes, but with me in office, I'll get it built, and Fast!" Trump tweeted on Monday afternoon.

It's unclear how Trump plans to get out of the partial shutdown that has hit hundreds of thousands of federal workers, since Democrats are disinclined to grant funding for his border wall.

He could have avoided the shutdown altogether had he agreed to sign on to a stopgap measure that passed the Senate last month and would have kept government open in the short term, but would not have funded the wall.

But the President backtracked under pressure from conservatives in the House and right-wing media commentators like Ann Coulter and Rush Limbaugh.

So to climb down now would risk similar condemnation and the possibility of a weakening of support among base voters on whom he depends for political viability, given his decision not to try to broaden his 2016 coalition.

With a weak but stable political standing -- between 40% and 45% approve of the job he's doing in most polls -- the President clearly understands that he needs to engineer a series of base-pleasing fights this year to keep his political foundation intact.

But as Democrats take over the House, they have little incentive to bail the President out -- at least until there is evidence that his tactic of branding them weak on border security is causing them political damage.

After all, Trump won election by saying Mexico, not US taxpayers, would pay for the wall. And he said he would be proud to shut down the government over the wall in a notorious Oval Office clash with Democratic leaders.

The next move in the saga will come later in the week, when Democrats put the ball back in the Republican court.

The soon-to-be Democrat-controlled House is expected to vote on six Senate spending bills and a stopgap measure to reopen the Homeland Security Department at its current funding levels until February 8, a Democratic aide told CNN Monday.

Although the temporary measure would maintain the current $1.3 billion in border security money, Senate GOP Majority Leader Mitch McConnell says he won't move any legislation until Trump signs off.

So both sides are staring at a dead end.

The calendar says 2019 -- but it's already 2020

Warren took the first plunge of the front-running Democratic pack, giving her a head start on the first quarter fundraising race that will be used to assess the viability of the top contenders. She is likely to find the field crowded very soon.

The Massachusetts senator carved out populist economic ground with her opening message, stressing her humble roots and wholesome family background and accusing billionaires and corporations of attacking the middle class.

Warren's strengths include long crusades against big banks and Wall Street titans, as Democrats seek a candidate that can loosen Trump's hold on working-class voters in the industrial Midwest in 2020.

"Corruption is poisoning our democracy," Warren said in a web video filmed in her kitchen, and then hit out at "bigotry and fear" in a sidelong reference to Trump.

Pundits are already questioning, however, whether Warren has missed her moment, will be viewed as too old at 69, or will be seen as too white at a time when a youthful and ethnic transformation is taking place in the Democratic Party.

Her effort to defuse Trump's attacks over her claims to Native American heritage last year with a DNA test was widely seen as botched and damaging to her candidacy by Beltway insiders.

Still, Warren has a jump on other rivals, possibly including California Sen. Kamala Harris, New Jersey Sen. Cory Booker and former Vice President Joe Biden.

The stirring Democratic race will also give Trump something he has long lacked, but loves -- a new enemy that he can use to define his own re-election bid and a genuine opening onto the campaign trail, where he excels.

The jockeying for position among Democrats and how the candidates respond to withering fire from Trump will define the first year of the 2020 campaign.

It's always Mueller time

A reminder of where we were before the holiday.

Trump's campaign, transition, inaugural committee and presidency are under active investigation. So are his business, the Trump Organization, and his defunct charity, the Trump Foundation. The President was indirectly implicated by New York prosecutors overseen by his own Justice Department in directing criminal attempts to subvert campaign finance laws.

Predictions that Mueller would wrap up his investigation into alleged election collusion with Russia and possible presidential obstruction of justice by the end of 2018 turned out to be wide of the mark.

But every week that went by late last year brought more bad news for Trump and signs Mueller is closing in on the President following a flurry of legal filings, court moves and convictions, and guilty pleas against close Trump associates.

Questions swirl around Trump's longtime political adviser Roger Stone, about, among other things, what he knew about WikiLeaks email dumps and when he knew it. And people even closer to Trump, such as his son Don Jr. and son-in-law Jared Kushner, cannot be sure they are in the clear, although all, including the President, profess innocence and downplay Mueller's investigation.

Rising pressure on the White House may have prompted Trump's lawyer Rudy Giuliani to escalate the effort to discredit the special counsel over the holiday.

"My ultimatum is put up or shut up, Bob," Giuliani said on "Fox and Friends" on Sunday.

"What do you have? There are those of us who believe you don't have anything on collusion," he continued. "And by the way, it's not a crime. So what the heck are you doing?"

Despite such defiance, Mueller could have the most fateful impact on the political year if he concludes that Trump has something to answer for in a report that could put the entire presidency in peril.

Turmoil in the West Wing

The first half of Trump's term has generated unprecedented turmoil, turnover and chaos in the West Wing. There's no reason to think that changes now.

The President enters the new year more liberated from "adults in the room" than ever, and freer to follow his impulses. What that means became clear late last year, with his sudden Twitter announcement of a full troop withdrawal from Syria with the words "they are coming back now."

The President's willingness to follow his gut was also reflected in his lurch into a government shutdown.

Yet in the days since, his improvisational governing style has sparked strategic confusion about his intentions on both issues.

After meeting the President for lunch on Sunday, South Carolina Sen. Lindsey Graham appeared to signal that Trump was having a change of heart at least about the pace of withdrawals from Syria.

On Monday, Trump hit out at comments by his departing chief of staff, John Kelly, who had suggested in an interview with the Los Angeles Times that the concept of a concrete wall had been abandoned long ago.

But before Christmas, the President tweeted that the wall would in fact be made up of "artistically designed steel slats" that border agents could see through.

The confusion is yet another sign that the President's often shifting positions and goals -- which he sees as the key to keeping his foes off balance -- will mean another year of political whiplash in Washington.