(CNN) A frenzied year in Washington is going out with a roar as the political forces that combined to make the first half of President Donald Trump 's mandate so turbulent come to a head in a hugely consequential run-up to the holidays.

Looming over everything is the new reality, fueled by weeks of court filings by special counsel Robert Mueller and other prosecutors, that every corner of Trump's public life is now under investigation: his White House, his campaign, his presidential transition, his inaugural committee, his businesses.

The President's sense of persecution prompted a rage-filled Twitter outburst on Sunday that also appeared to reflect concern about cooperation agreements secured by Mueller with his longtime personal attorney and fixer Michael Cohen and former national security adviser Michael Flynn.

"The Russian Witch Hunt Hoax, started as the 'insurance policy' long before I even got elected, is very bad for our Country," Trump tweeted.

"They are Entrapping people for misstatements, lies or unrelated things that took place many years ago. Nothing to do with Collusion. A Democrat Scam!"

....The Russian Witch Hunt Hoax, started as the "insurance policy" long before I even got elected, is very bad for our Country. They are Entrapping people for misstatements, lies or unrelated things that took place many years ago. Nothing to do with Collusion. A Democrat Scam! — Donald J. Trump (@realDonaldTrump) December 16, 2018

Trump's tweet ignored the fact that the legality of the Mueller probe has been upheld in court on several occasions and that it has secured a number of convictions and is opening a window into the President's own behavior in its prosecutions of his associates.

Former FBI Director James Comey, whom Trump fired, laid into the President in his own tweet Sunday, dismissing the President's claim on Twitter that the bureau's raid against Cohen this year was illegal.

"This is from the President of our country, lying about the lawful execution of a search warrant issued by a federal judge. Shame on Republicans who don't speak up at this moment — for the FBI, the rule of law, and the truth," Comey wrote.

This is from the President of our country, lying about the lawful execution of a search warrant issued by a federal judge. Shame on Republicans who don't speak up at this moment — for the FBI, the rule of law, and the truth. pic.twitter.com/c5dhQBnmyi — James Comey (@Comey) December 16, 2018

As a new week dawns, the capital is on edge to see whether Mueller has any more dramatic cards to play before the turn of the year. One event that may further irritate the President is Tuesday's sentencing hearing for Flynn, who admitted lying to the FBI.

But the Russia investigation is only one element in a complex set of political dramas that are playing out before Washington breaks for the Christmas and New Year recess.

An impasse over Trump's border wall could shutter parts of the government by the end of the week -- the latest battle in the war over immigration that has rocked American politics for more than a decade.

Yet another Cabinet member, Interior Secretary Ryan Zinke, is going home trailed by scandal, in another rebuke to the idea that the Trump administration was ever about draining the swamp.

A fresh staff shakeup is playing out in the West Wing, but experience suggests that new acting chief of staff Mick Mulvaney will fare no better than his predecessors in imposing order on a President who defies management.

Obamacare is having another brush with extinction in the courts, just as the Republican House majority built on a vow to overturn the law limps out of town.

And the Democratic majority that will take over the House next year is already flexing its muscles after an extraordinary televised showdown between the party's top brass and Trump last week offered a preview of skirmishes to come.

The President's biggest, indisputable success is the motoring economy and historically low unemployment. But there are growing fears after several volatile weeks that a slowdown is looming, given ebbing global growth, a trade war with China and churning market volatility.

White House 'absolutely' ready for a shutdown

The possibility of a partial shutdown when funding runs out for several key departments at the end of the week appeared to rise on Sunday, with the White House and top Democrats hunkering down over Trump's demand for $5 billion in border wall funding.

"We're going to do whatever is necessary to build the border wall to stop this ongoing crisis of illegal immigration," White House senior policy adviser Stephen Miller said on CBS's "Face the Nation."

Asked whether that meant forcing a shutdown to extract the funds from Congress on an issue that was foundational to Trump's presidential campaign, Miller replied, "If it comes to it, absolutely."

But Senate Minority Leader Chuck Schumer said Trump will not get what he wants.

"President Trump should understand, there are not the votes for the wall. In the House or the Senate, he is not going to get the wall in any form," Schumer said on NBC's "Meet the Press."

Signs that the gap between the White House and Democrats is deepening raise the possibility that the showdown, if it does shutter government, could develop into the first big clash between the new Congress and the White House in January.

New trouble for Obamacare

Americans who rely on the Affordable Care Act got a surprise lump of coal late on Friday night when a federal judge in Texas ruled that the entire law was unconstitutional.

The move set off a fresh duel over the centerpiece of Barack Obama's domestic agenda that has so far defied all GOP attempts to kill it off.

Immediate legal opinion — even from some conservatives — suggested that the sweeping ruling could end up being overturned, though there is a chance the fight over Obamacare's fate could end up yet again in the Supreme Court in a test of the new conservative majority.

The decision reignited the political wars over health care that Democrats believe played a significant role in their surge to victory in the House in the midterm elections. If that is the case, the Obamacare ruling, paradoxically, may not be good news for the GOP.

But Trump welcomed the latest threat to his predecessor's legacy.

"I believe we're going to get really good health care. Exciting things happened over the last 24 hours," Trump said at a congressional ball at the White House on Saturday night. Typically though, he gave few details of his vague plans to provide a better alternative to Obamacare, which now looks likely to be a key issue in yet another national election cycle.

Swamp creatures

Trump enters another week looking for another new Cabinet member after announcing the resignation of Zinke, who was facing multiple ethics probes and was a top oversight target of the new Democratic House.

The New York Times and Washington Post also reported that Zinke might have been fired if he failed to quit by the end of the year.

Possible replacements include Deputy Interior Secretary David Bernhardt and Nevada Republican Sen. Dean Heller, who lost his re-election race, sources with knowledge of the situation said.

Mulvaney, meanwhile, is gearing up to take on the daunting task of being Trump's third chief of staff. Given the failure of his two predecessors, Reince Priebus and John Kelly, to rein in a President who trusts his gut above all, there are few expectations that Mulvaney will calm an often erratic White House and impose discipline, as many predecessors did in other administrations.

"He's the chief of staff, not chief of the President, right? That's an important distinction," David Urban, the political strategist who masterminded Trump's 2016 victory in Pennsylvania, said on CNN's "State of the Union."

Still, Mulvaney appears to have a trusting relationship with the President, following his tenure as his budget chief. And his knowledge of Capitol Hill, gained as a former member of the House, will be an asset as the White House seeks to outmaneuver would-be Speaker Nancy Pelosi and her troops next year.

Russia to overshadow Trump's Christmas

Trump heads into a Christmas break at his Mar-a-Lago resort this week in a position of increasing political and legal vulnerability after weeks of devastating revelations and court filings related to the Russia investigation.

The President has been implicated by New York prosecutors overseen by his own Justice Department in directing criminal attempts to subvert campaign finance laws alongside Cohen, whose case was referred by Mueller.

Cooperation by Cohen and Flynn is helping Mueller take his investigation deep into the President's inner circle. He has now uncovered multiple contacts between Trump associates and Russians during the time of Moscow's election meddling effort and repeated lying about those encounters.

Speculation is frenzied about one mysterious scene on Friday in which an entire floor of the federal courthouse in Washington was locked down over a mystery subpoena appeal involving the special counsel's team.

Things are certain to become more uncomfortable for Trump in the new year. Maryland Democratic Rep. Elijah Cummings, who is expected to take over the House Oversight and Government Reform Committee, said on "State of the Union" that he would seek to secure testimony from Cohen before the President's former fixer reports to prison in March.

There were also worrying signs for Trump in a new NBC/Wall Street Journal poll that found that 62% of respondents believe the President has not been truthful about the Russia investigation.

Since his approval rating was 43% in the survey however, it seems that a portion of those Republicans who are uneasy about the President's attitude toward Mueller still don't see it as a deal breaker for their faith in him.