Updated May 8, 4:50pm.

Donald Trump and his White House are blocking congressional oversight, withholding information, and forbidding former officials from testifying.

The Department of Justice is moving to protect the president from further investigation.

Republicans say they can’t pass bills that impact millions of Americans desperate for economic support because of Trump’s intransigence on tariffs and budgets.

In each case, Trump appears to be reaching for authority rarely granted to presidents—and seeing little pushback.

The US has entered a constitutional crisis, a growing number of historians and government officials say, as Trump and his administration defy protocol in new ways. “We’ve talked about avoiding a Constitutional crisis. We are now in it,” House Judiciary chair Jerrold Nadler said this afternoon, as the committee voted 24-16 to hold Attorney General William Barr in contempt of Congress.

“We are in the worst crisis that American democracy has ever had,” said Heather Richardson, a history professor at Boston College who traces the evolution of the Republican Party.

Richardson contends that if the Republicans who controlled both houses of Congress for the first two years of Trump’s presidency had “nipped in the bud” his overreach in his first weeks in office, “we would not be where we are.” Instead, Trump spurned US allies, appeared to profit from the presidency, and gained more confidence in running the White House like his own private company.

“The problem with a leader like Trump is they cannot stop”

“The problem with a leader like Trump is they cannot stop,” Richardson said. “It is oxygen to them to keep pushing the limit. The only way he can feed not just his base but himself is to keep upping the ante.” And Trump’s popularity among Republicans remains as strong as ever.

Trump’s most radical departures from precedent—from attempting to deport longtime US residents to gutting the Barack Obama’s Affordable Care Act—have been challenged in the courts by state attorneys general and civil-rights groups. His latest moves set up an even more dramatic battle between the branches of US government, one the Constitution was not designed to handle, academics and experts fear.

Several matters now in motion could trigger a constitutional crisis for an America not designed for a Donald Trump presidency. Here is a look at the most-serious issues in play, and what might come next for each:

The White House defies Congress

Trump is challenging Congress’s mandated oversight of the executive branch. He exerted “executive privilege” over the FBI special counsel Robert Mueller’s entire special report May 8, essentially blocking all of Congress from reading its redactions and underlying evidence. Trump is also suing to block any release to Congress of information about his finances and the Trump Organization’s by the private companies that hold it, and has instructed former White House counsel Don McGahn not to comply with Congress.

Cabinet members and the Department of Justice are aiding him by stonewalling lawmaker’s requests. Barr laid out the argument for executive privilege in a May 8 letter, after refusing to testify to the House Judiciary committee. Treasury secretary Steve Mnuchin has refused to turn over Trump’s tax returns, as requested by Democrats, because the request “lacks a legitimate legislative purpose.”

Meanwhile, Trump’s oldest son, Donald Jr. was issued a subpoena May 8. to appear before the Senate Intelligence Committee.

Government watchdogs, legal experts and former DOJ officials say Trump and his appointees do not have the right to make any of these decisions unilaterally. Trump’s May 8 tweets about a New York Times article detailing enormous losses he claimed on his federal taxes give Congress new “legitimate legislative purpose, not that several didn’t already exist,” said George Conway, the conservative attorney who believes Trump is undermining the US rule of law. “Thank you, Mr. President.” (Trump supporters say Congress is using the Treasury’s Internal Revenue Service as a “political weapon.”)

“The thing that’s unusual is the blanket refusal”

Like Barr, US attorneys general have clashed with Congress before, and even been given contempt citations. But this battle is different, legal experts and former federal officials say. “The thing that’s unusual is the blanket refusal,” to give Congress any information, John Yoo, the former George W. Bush administration official who penned the so-called “torture memos” defending giving the president broad powers in that area, told the New York Times.

Trump’s attempt to prevent Congress from looking into his financial ties and his activities as candidate and president “goes far beyond anything [Richard] Nixon did,” former Watergate special prosecutor Nick Akerman told Beltway Breakfast, adding that even the only president to resign never rejected the authority of Congress just because it was controlled by the opposing party.

“According to Trump, there is to be no congressional oversight of this administration,” writes Robert Reich, a professor of public policy at the University of California at Berkeley who was labor secretary in Bill Clinton’s administration. “Such a blanket edict fits a dictator of a banana republic, not the president of a constitutional republic founded on separation of powers.”

WHAT’S NEXT? The entire House votes next on whether to hold Barr in contempt; the House Judiciary may do the same for McGahn in days to come. It is also considering an amendment expressing “disappointment” in Trump’s executive privilege demands, a relatively toothless measure.

A judge who hears a contempt case could rule the officials should testify. But “recent controversies could be interpreted to suggest that the existing mechanisms are at times inadequate,” the Congressional Research Service wrote this March, “particularly in the instance that enforcement is necessary to respond to a current or former executive branch official who has refused to comply with a subpoena.”

“My biggest fear is that if it were to go to court, and the court were to affirm Congress’ authority, that the president would simply refuse,” Victoria Nourse, Georgetown University law professor and director of the Center on Congressional Studies, told the Associated Press. That scenario would be “a true constitutional crisis” she said, that could only be resolved by impeachment.

Doubt surrounds Barr

Barr has already been accused of acting like Trump’s personal attorney by Democrats, and now hundreds of former Department of Justice officials are now echoing the criticism.

About 800 former federal prosecutors from both parties signed a letter released May 6 that criticizes Barr’s handling of Mueller’s report, particularly the attorney general’s conclusion that there was not enough evidence to pursue charges of obstruction against Trump.

Trump’s conduct would “result in multiple felony charges for obstruction of justice” if he was anyone else

“The conduct of President Trump described in special counsel Robert Mueller’s report would, in the case of any other person not covered by the Office of Legal Counsel policy against indicting a sitting President, result in multiple felony charges for obstruction of justice,” the letter states.

WHAT’S NEXT? Demands are growing for Barr’s conduct to be investigated more fully by Congress. Some Democrats in the House are even talking openly about using their own sergeant-at-arms to arrest him if he is found in contempt. House speaker Nancy Pelosi hasn’t ruled out impeaching him.

Trump holds up key Senate votes

Even as the White House wages war with House Democrats, it’s also defying leaders of its own party, in ways that are affecting governance. Presidents have disagreed with Congress before over legislation, and “gridlock” over partisan fighting is nothing new in Washington DC. Yet the dysfunction now is mostly Trump standing in the way of benefits for his own voter base.

A disaster-relief bill that would deliver $14 billion in desperately needed funds to farming states including Republican strongholds Nebraska and Iowa, is being held up in the Senate because Trump wants another $4.5 billion for immigration-related projects on the southern border, appropriations committee chair Richard Shelby, a Republican, told journalists May 7.

Sheby doesn’t expect things to get better in months to come. “This is a preview of a coming attraction,” Shelby said, referring to difficult fights ahead to pass broader spending bills to fund the government, a chilling prediction just months after the US’s longest-ever government shutdown. “We’ve got real problems.”

Senate Republicans are refusing to consider Trump’s updated North American Free Trade Agreement, called USMCA, because the White House refuses to lift steel and aluminum tariffs. The bill “isn’t going to come up in [this] environment,” Iowa Republican Chuck Grassley said May 6. Until it does, many US companies’ relationships with their largest trading partners remains in limbo.

The Department of Homeland Security is drafting rules to allow 30,000 foreign workers to come into the US on a temporary basis, the AP reported this week, blindsiding Republicans who have embraced Trump’s “tough on immigration” agenda. “We should be setting immigration policies that support wage growth and employment for Americans instead of encouraging a race to the bottom by importing low-cost labor,” complained Tom Cotton, the Arkansas senator.

WHAT’S NEXT Republicans have dug in on the steel and aluminum tariffs, and the White House is trying to save China trade negotiations that have roiled the stock markets. Meanwhile, US pork producers are losing business to Mexico. Trump meets with Republican senators today on immigration. The focus is expected to be on a vague, broad Jared Kushner plan to revamp US policy that’s not expected to garner much support in Congress.

And Trump’s approval rating rises

The White House’s shunning of historical protocol started at the outset of Trump’s term, giving rise to a debate about whether US presidents had acquired too much power.

So far, it’s not hurting Trump at the polls —his approval ratings are at their highest level ever, at 46%, according to a new Gallup poll taken in the second half of April. Trump is gearing up for the 2020 election, and portraying himself as a beleaguered underdog is part of his re-election strategy.

American governance, though, is suffering. Protect Democracy, a non-partisan group that pledges to use the Constitution and the rule of law to “fight back and protect our democracy from those who would do it harm,” assesses the “threat level” for the US democracy at 41 out of 100.

The American system is now marked by “violations that signal significant erosion of democratic quality and warn of high potential for breakdown in future,” the group warns.

WHAT’S NEXT? House Democrats are debating whether to start impeachment proceedings against Trump or not. (Though it may be even something he would welcome.) How effective that process will be if the White House refuses to respond to requests for information is unclear. “The sticking point is who is going to stand up and say ‘This is not OK’,” Richardson said.