When Congress reconvenes in 2019, Democrats will hold the majority in the House – setting up potential contentious legislative battles with President Trump.

With control, Democrats will head up House committees, controlling investigations and handling calls for impeachment. The incoming House Ways and Means Committee chairman might also request Trump’s tax returns.

Read on for a look at seven congressional leaders who are sure to be a thorn in Trump’s side.

Judiciary Committee – Jerry Nadler

As the incoming chair of the House Judiciary Committee, Rep. Jerry Nadler will lead the panel that could begin the process to impeach Trump. But Nadler, a New York Democrat, has remained consistently cautious when it comes to calls for impeachment – saying it is essentially “overturning the result of the last election.”

“You don’t want to have a situation where you tear this country apart and for the next 30 years half the country’s saying, ‘We won the election, you stole it,’” he told Roll Call.

In November, Nadler said calls for impeachment were “premature.” But he seemed to waver a bit earlier this month when he said if it’s proven Trump directed his former lawyer to commit campaign finance violations – as was suggested by special counsel Robert Muller in a court filing – it could be an impeachable offense. However, he added, “Whether they are important enough to justify an impeachment is a different question.”

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Aside from impeachment, Nadler, 71, has promised the committee won’t “try to shield the president” but will instead continue to look into questions about whether Trump lied about his business arrangements with Russians and potential obstruction of justice. Russian interference in U.S. elections, particularly the 2016 election, will also be on his agenda, according to Roll Call.

Additionally, the Judiciary Committee also tackles immigration – setting up another potential kerfuffle between the Trump administration and House Democrats.

Oversight Committee – Elijah Cummings

As the incoming chairman of the Oversight Committee, Rep. Elijah Cummings, D-Md., is set to have broad investigative power in the House – and he’s already hit the ground running.

In December, Cummings sent 51 letters to various federal agencies and the White House requesting documents about security clearances, the Trump Organization’s work with foreign entities and scandals that plagued the Environmental Protection Agency when Scott Pruitt was at its helm.

In his request, Cummings, 67, noted the committee’s Republicans had previously requested such documents but “the Trump administration refused to comply.”

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“As Democrats prepare to take the reins in Congress, we are insisting – as a basic first step – that the Trump administration and others comply with these Republican requests,” Cummings said in a statement.

Cummings previously told Politico Magazine his focus will be on “getting documents” since he doesn’t trust what members of the administration say.

“Let’s cut through the unnecessary BS and let’s get to the facts — and I do not want anybody wasting my time. Nor do I want to waste the time of my committee members or my family members,” Cummings said. “And I damn sure don’t want to waste my time.”

House Ways and Means Committee – Richard Neal

Massachusetts Rep. Richard Neal has his eyes on Trump’s tax returns. The 69-year-old Democrat has been voted to lead the House Ways and Means Committee – potentially giving him the authority to request the president’s tax returns.

Despite saying he will have “the ability to ask for the president’s tax returns,” Neal has contended there would most likely “be a court case that goes on for a period of time,” according to The Republican.

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Aside from Trump’s tax returns, Neal could also set up a testy feud with the administration through protecting ObamaCare or battling Trump’s trade policies.

Intelligence Committee – Adam Schiff

As the chair of the House Intelligence Committee, Rep. Adam Schiff, D-Calif., hopes to protect Mueller’s Russia probe.

In an interview with NPR, Schiff specifically said he wanted to look into conversations Donald Trump Jr., the president’s oldest son, had with a Russian official as well as potential money laundering by Russians through the Trump Organization.

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Like Nadler, Schiff, 58, has also been leery about overzealous calls for impeaching Trump. He has said Congress should wait “until we see the full picture,” especially as his committee would probe the Trump family’s business ties with Russia.

“I think we also need to see this as part of a broader pattern of potential misconduct by the president, and it’s that broad pattern, I think, that will lead us to a conclusion about whether it rises to the level to warrant removal from office,” he has said.

Trump and Schiff have already gone head-to-head, with the president dubbing the congressman “Adam Schitt” and “sleazy” on social media.

Armed Services Committee – Adam Smith

Washington Rep. Adam Smith already plans to push back against some of the Trump administration’s proposals when he assumes the chairmanship of the House Armed Services Committee – pointing specifically to border security and the “Space Force.”

Trump “misunderstands the problem” at the border, Smith said after a recent breakfast, according to The Daily Herald. The congressman also chastised Trump for deploying troops to the U.S.-Mexico border ahead of a caravan of migrants expected to try to cross into the U.S. for asylum, calling it a “misuse of our troops.”

“The challenge we are facing now is different,” Smith, 53, said. “It’s asylum seekers. You don’t need to build more security because folks are not trying to sneak in. They are turning themselves in [to get] through the process. I don’t deny there has been a significant increase in people seeking asylum, but the solution to that is not to harden the border. The solution is to hire more judges and expedite the process.”

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As for Trump’s call for a new “Space Force” military branch, Smith said there remains “bipartisan concern about creating a separate branch of the military,” including among some Defense Department officials.

Smith previously said he hoped Congress and the committee could “step in where the White House has stepped back to make sure our military is not engaged in ways” not in the country’s best interests.

Foreign Affairs Committee – Eliot Engel

With Rep. Eliot Engel at the helm, the House Foreign Affairs Committee plans to probe interactions between the White House and the Trump Organization with foreign entities, according to The Washington Post.

“The White House needs to take us seriously, and if they don’t, we are going to make sure they take us seriously,” the New York Democrat told the newspaper, adding he “intend[s] to use every prerogative that I have to ensure oversight.”

Engel, 71, said the committee has failed to provide proper oversight in recent years, and he hopes to change that.

“What disturbs me is Trump’s fly-by-the-seat-of-the-pants diplomacy,” he told The Journal News. “Whatever he tweets out becomes policy.”

Appropriations Committee – Nita Lowey

New York Rep. Nita Lowey is expected to chair the powerful House Appropriations Committee, the group that controls discretionary funding. And already she’s said she’ll put a wrench into one of Trump’s biggest political promises: the border wall.

“We are not funding Trump’s border wall,” Lowey told The Journal News. “We will invest in other programs that make us safer.”

After the Democratic Caucus elected the 81-year-old to serve in the chairmanship position, Lowey vowed to “make government work for the people.”

“I am also committed to using Congress’s constitutional power of the purse to provide robust, effective oversight of the Trump Administration and to reject funding that runs counter to the values and interests of hardworking families,” she said.

The Associated Press contributed to this report.