(CNN) The reckoning that has been due for the Trump administration ever since Democrats won the midterm elections is about to hit with full force, with a multi-front oversight offensive targeting the President and his senior officials.

A round of congressional action and hearings will take place with President Donald Trump out of the country, in Vietnam for a second summit with North Korean leader Kim Jong Un, though he is expected to follow developments closely on television.

Almost at the same time as Air Force One rolled to a stop at the airport in Hanoi Tuesday, Trump's former personal lawyer Michael Cohen arrived on Capitol Hill at the start of three days of testimony that could inflict severe political damage on the President and will feature a hugely anticipated open House hearing on Trump's personal and business history on Wednesday.

The Democratic oversight effort is intensifying after Deputy Attorney General Rod Rosenstein unleashed a Washington firestorm Monday by warning of the dangers of a surfeit of transparency as the special counsel's investigation draws to a close.

Top Democrats immediately warned of double standards after a torrent of disclosure orchestrated by Republicans related to investigations into Hillary Clinton, and vowed to use their power to ensure full disclosure.

"For two years, I sounded the alarm about DOJ's deviation from just that principle as it turned over hundreds of thousands of pages in closed or ongoing investigations. I warned that DOJ would need to live by this precedent," Rep. Adam Schiff, the California Democrat who's the chairman of the House Intelligence Committee, wrote on Twitter.

"And it will."

The unexpected controversy came as another shock to taut nerves in the capital at a fateful moment, with special counsel Robert Mueller expected to soon hand over the results of his probe into Russian election interference to Attorney General Bill Barr.

The confrontation between the White House and Democrats beginning to unsheathe the power of their new House majority was already going to be ugly, as a flurry of hearings and floor action this week will demonstrate.

The Democratic House majority will hold a vote Tuesday on a historic attempt to terminate the national emergency that Trump is using to try to go around Congress after it refused to fund his border wall.

"To do anything less than overturn this action by the President, we would be delinquent in our duties," House Speaker Nancy Pelosi said during a trip to the border last week.

Cohen, who will head to jail to begin serving a three-year sentence later this year, will appear in private before the Senate Intelligence Committee on Tuesday.

Emotional exchanges are expected meanwhile in a House hearing that will question officials about the administration's suspended practice of separating undocumented migrant children from their parents at the Mexican border.

It is almost certain that none of the congressional scrutiny that will play out over the next few days would have happened during the previous, pliant GOP-led House majority, which had no inclination or incentive to check the President.

The confrontations are likely to offer a preview of the next two years in Washington, with little sign of serious bipartisan legislating on the horizon and both sides already using the clashes to position for the 2020 White House race.

They will also test the capacity and willingness of Republicans, especially in the Senate, to defend the President, even on an issue like the national emergency declaration, which has troubled some GOP members on constitutional grounds.

Trump's willingness to meet Kim -- at the same time he is laying plans for a summit with Chinese leader Xi Jinping to consummate a trade deal -- sends its own eloquent signal.

Even as Democrats step up broad efforts to rein in Trump's power, the President will seek to maximize every opportunity to wield executive authority that may be beyond Congress' power to constrain.

Both sides leverage Washington clash in 2020 fight

Democrats understand that their attempt to use a provision in the 1976 National Emergencies Act is unlikely, in the end, to triumph over a certain presidential veto, owing to GOP strength of numbers in the Senate.

One Republican senator, for instance, who once expressed some concern about the use of emergency authority to build the wall, John Cornyn of Texas, appears to be sizing up political considerations now that the debate is a reality.

"I am leaning against the resolution of disapproval mainly because I think this is (Senate Minority Leader) Schumer's and Pelosi's way of painting the President in the corner," Cornyn said Monday.

"He said all along he wanted money to do border security and they basically (said) we're determined not to give him what he thought was necessary."

Still, several other GOP senators have expressed disquiet about Trump's move, so it is possible the resolution of disapproval could pass the Senate the first time around, even if a veto-proof majority is out of reach.

The Democratic stand offers a preview of the arguments that will unfold when the declaration is challenged in a legal battle that could go all the way to the Supreme Court.

And it will serve a political purpose as Democrats seek to leverage an issue on which they have public opinion on their side -- opposition to using an emergency decoration to build the wall -- to weaken the President.

There is a common thread running through all the Democratic congressional oversight efforts. They represent a genuine attempt to use power that party leaders believe was granted by voters in November to rein in a President who often strains at the limits of his office.

The use of checks and balances also allows Democrats to build a case to lay before the public -- that the Trump presidency represents a legal and moral departure from American values -- that will underpin their 2020 campaign.

That idea will be the implicit message that Democrats will try to extract from a House Judiciary Committee hearing on Tuesday into family separations that critics branded as cruel and inhumane during a showdown over the practice last year.

Among the witnesses will be Scott Lloyd, the former director of the Office of Refugee Resettlement, the highest level official yet challenged on the separations under the new Democratic majority.

Health and Human Services Secretary Alex Azar declined a request to testify on Capitol Hill earlier this year.

The administration came under increased pressure over the "zero tolerance" immigration policy following the release of an HHS inspector general's report that found thousands more children had been separated from their parents than had previously been acknowledged.

Of the more than 2,000 children who have been identified, many have been reunited with their parents, according to recent court filings.

Out of sight -- not out of mind

Given his penchant for setting the political agenda, on Twitter or via encounters with reporters, it's unlikely the President will be able to resist weighing in on the political collisions in Washington.

In fact, he will sit down for dinner with Kim on Wednesday evening in the Vietnamese capital at about the same time -- given the 12-hour time difference -- that Cohen will appear before the House Oversight Committee.

With this President, out of sight is never out of mind.

A more conventional commander in chief might choose to avoid the drama back in Washington to keep the focus on his high-stakes foreign policy gambit and avoid giving a story that is unfavorable to him more legs.

But Trump always responds when he believes he's been attacked -- often in more cutting rhetoric than that used against him.

He is almost certain to brand Cohen a liar, since his former attorney has already admitted not telling the truth to Congress, even though any counterattack risks drawing attention and headlines from his head-to-head with Kim.

Cohen's appearance is likely to be seen by Trump as an act of betrayal, amid indications from the committee that he will testify about the President's business and personal life in a way that could damage his former client.

He is also certain to be asked about accusations that the then-Republican presidential nominee ordered him to pay hush money to two women who claimed they had affairs with Trump because he was worried about the impact of the scandal on the 2016 election.

The President's son Don Jr. got some retaliation in first Monday in a likely preview of the administration's defense.

"You've got a President trying to deal with a major world issue and you are trying to distract or whatever it is by bringing in a convicted felon and known liar," Trump Jr. said on Fox News.

"It is pretty pathetic but it really shows you how much the Democrats hate Trump," he said.

However Trump navigates the split-screen moment of the next few days, the accelerating Democratic oversight campaign represents a serious challenge to the White House -- and subpoenas haven't started flying yet.

Relentless scrutiny by the other party in Congress is exhausting and demoralizing for an administration as officials get hauled up to testify and face their own individual legal threats.

But Trump seems to have lived his entire life in an atmosphere of chaos and on a personal knife edge.

The President has already sought to brand the Democratic oversight strategy as "presidential harassment." And he has never been more dangerous politically than when he has a foil.