Welcome to Donald Trump’s nightmare.

When the 116th Congress is sworn in on Thursday, the Democratic Party will control the House of Representatives ― and the new committee chairs are ready to finally conduct rigorous oversight of the president’s administration for the first time.

“For the last two years, the president has had no oversight, no accountability from Congress,” Rep. Jerry Nadler (D-N.Y.), the new chairman of the House Judiciary Committee, said on “CBS This Morning” on Wednesday. “We’re going to provide that oversight. We’re going to use the subpoena power if we have to.”

Democrats will almost immediately begin to investigate the many controversial policies and scandals of the Trump administration.

Anti-Immigrant Policies

Nadler has promised to dig into the president’s nativist policies targeting refugees, migrants and immigrants already living in the United States. This includes getting real answers about the administration’s family separation policy that ripped migrant children from their parents at the border and investigating the inclusion of a citizenship question in the 2020 Census, the deployment of U.S. troops to the border and changes to asylum laws.

Rep. Elijah Cummings (D-Md.), the new chairman for the House Oversight and Reform Committee, also plans to immediately send out document requests and subpoenas to get to the bottom of the family separation policy. His Thursday letter will demand the Department of Health and Human Services, Department of Homeland Security and Department of Justice provide documentation on every child who was separated from their parents at the border and where they are now.

Security Clearances For Flynn And Kushner

Cummings also plans to ask the White House to explain how it approved security clearances for former national security adviser Michael Flynn and Trump’s son-in-law, Jared Kushner. Flynn pleaded guilty to lying to the FBI about his contacts with the Russian ambassador during the transition in 2016 and for failing to file as a foreign agent for the government of Turkey. Like the president, Kushner retains a connection to his family real estate business, which has extensive debts and interests linked to foreign countries ― a major potential conflict of interest.

ASSOCIATED PRESS Rep. Elijah Cummings (D-Md.), left, and Rep. Jerry Nadler (D-N.Y.), right, will lead investigations into the Trump administration from their respective posts as chairman of the House Oversight and Reform Committee and House Judiciary Committee.

Trump’s Corruption

The president’s many conflicts of interest will also come under the microscope. His refusal to divest from his business means that he still makes money when lobbyists, big corporations and foreign governments pay to use his properties. Trump’s involvement in the decision not to move the FBI headquarters in downtown Washington, D.C., has also raised concerns about a conflict of interest as the building is across the street from the president’s hotel. Cummings and Rep. Peter DeFazio (D-Ore.), the new chairman of the House Transportation and Infrastructure Committee, will investigate these conflicts.

The House Ways & Means Committee plans to obtain Trump’s tax returns ― although maybe not immediately. Trump was the first major party presidential candidate since Richard Nixon to refuse to disclose his tax returns to the public. A New York Times investigation found that Trump likely committed tax fraud with his father, Fred Trump, when the elder Trump transferred nearly half a billion dollars to his son in a manner that evaded taxes.

“There is popular demand for the Congress to request the president’s tax returns,” Democratic leader Nancy Pelosi (D-Calif.) said in December.

Trump’s Sidekicks

Almost every House committee will have the ability to dig into the widespread corruption that has characterized the Trump administration across practically every agency. Former Interior Secretary Ryan Zinke’s conflict-ridden land deals with the oil-services company Halliburton and the casino operator MGM can be investigated now. Secretary of Housing and Urban Development Ben Carson’s nepotism and cronyism are also fair game, as is the elevation of Matthew Whitaker from a non-Senate-confirmed aide who recently worked as a salesman for a company convicted of fraud and a pitchman for toilets designed for men with oversized genitals to the position of acting attorney general.

“I want to probe senior Administration officials across the government who have abused their positions of power and wasted taxpayer money, as well as President Trump’s decisions to act in his own financial self-interest rather than the best interests of the American people,” Cummings previously told HuffPost.

‘Presidential Harassment’

Trump has already attempted to deflect these investigations by labeling them “Presidential Harassment,” a phrase initially coined by Senate Majority Leader Mitch McConnell (R-Ky.).

Although every president has complained about congressional investigation, the practice of congressional oversight of the executive branch dates back to President George Washington’s first term. In recent years, investigators have taken varying approaches from properly investigating policies and abuses to engaging in political theater and conspiracy mongering.

Former Rep. Dan Burton (R-Ind.) famously used his control of the oversight committee in the 1990s to follow every rumor and conspiracy theory about President Bill Clinton, whom he declared “a scumbag.” Burton believed that Clinton had ordered the assassination of White House lawyer Vince Foster (Foster committed suicide in 1993) and even re-enacted the invented murder by shooting a cantaloupe (or maybe a pumpkin or a watermelon) in his backyard.

In the 2000s, Rep. Tom Davis (R-Va.) and Rep. Henry Waxman (D-Calif.) separately helmed the oversight committee and undertook serious investigations of the George W. Bush administration ― often with bipartisan support. Davis helped investigate the Jack Abramoff lobbying scandals, while Waxman investigated the 2008 market crash and the lies that led the U.S. to invade Iraq.

ASSOCIATED PRESS President Donald Trump has taken to calling any efforts by Democrats to investigate his administration "Presidential Harassment."

Under Obama, Republican Darrell Issa (Calif.) wielded the oversight gavel in a unilateral manner by sending out more subpoenas than the previous three chairmen combined. Meanwhile, Rep. Trey Gowdy (R-S.C.), the outgoing oversight chairman, led a special committee to investigate the death of Ambassador Chris Stevens and three other Americans during an attack in Benghazi, Libya. The investigation uncovered nothing new that multiple previous investigations had not revealed. Instead, the committee was used as a campaign tool against 2016 Democratic presidential candidate Hillary Clinton, who was Secretary of State at the time of Stevens’ death.

“Everybody thought Hillary Clinton was unbeatable, right?” Rep. Kevin McCarthy (R-Calif.) admitted in 2015. “But we put together a Benghazi special committee, a select committee. What are her numbers today?”

The committee disbanded one month after Clinton lost the election.

Democrats hope to avoid the perception that their investigations are solely for political or electoral advantage — even if nothing will stop the president from labeling anything investigating him a “witch hunt.” That is one reason why the new committee chairs are reluctant to engage in any incipient discussions about impeachment.

Special counsel Robert Mueller’s investigation into whether the president conspired with foreign countries including Russia to influence the 2016 election to his benefit has already netted numerous high-profile guilty pleas of Trump’s national security adviser, foreign policy aide and his personal lawyer and fixer. It has also led to the revelation that Trump lied during his campaign that he “had nothing to do with Russia” when he actually pursued a deal with the Russian government to build a Trump Tower in Moscow up until June 2016.

The special counsel’s investigation is still ongoing. Democrats are willing to wait to see its conclusions before they start talking about impeachment.

“There’s certainly a lot of allegations, but we’ll have to wait and see what the Mueller investigation comes up with and other investigations looking into it,” Nadler told CBS on Wednesday.