WASHINGTON (Reuters) – Armed with subpoenas and a long list of grievances, a small group of lawmakers will lead the investigations poised to make President Donald Trump’s life a lot tougher now that Democrats have won a majority in the U.S. House of Representatives.

Using their control of House committees, they can demand to see Trump’s long-hidden tax returns, probe possible conflicts of interest from his business empire, and dig into any evidence of collusion between Russia and Trump’s campaign team in the 2016 election.

Representative Elijah Cummings, who is expected to take over the House Oversight Committee, has said Republican lawmakers will no longer be able to protect Trump from a watchful Congress.

“The most important thing for the Oversight Committee to do is to get back to regular order by obtaining documents and interviewing witnesses, and actually holding the Trump administration accountable to the American people,” Cummings told Reuters.

He is one of three prominent Democrats who have clashed with Trump and will take over committees that will pressure his White House when the new Congress takes office in January.

The others are Jerrold Nadler, who will almost certainly head the House Judiciary Committee and was once described by Trump as “one of the most egregious hacks in contemporary politics,” and Adam Schiff of the Intelligence Committee, slammed by the president as “sleazy.”

Control of the committees – where they are currently the highest-ranking Democrats – will give those lawmakers the power to demand documents and testimony from White House officials and key figures in Trump’s campaign team and businesses, and to issue subpoenas if needed.

They will also have more money and staff for investigations that could delay or derail Trump’s agenda.

“I’m convinced he (Trump) has no idea what’s about to happen: the fact that the House now has wide-ranging authority to investigate every inch of his administration. He’ll deny six ways to Sunday that anything’s going to change, but the reality is that his world’s turned upside down as of this evening,” said Jim Manley, a Democratic strategist.

The White House can respond to committee demands by citing executive privilege in some circumstances, but that will likely result in court battles.

A first salvo in the battle is expected to come from Representative Richard Neal, the likely Democratic chairman of the tax-writing House Ways and Means Committee.

He has not publicly clashed with Trump in the way Nadler, Schiff and Cummings have, but Neal has vowed to demand Trump’s tax returns from Treasury Secretary Steven Mnuchin.

Such a move could set in motion a cascade of probes into any disclosures the documents might hold.

Even before the election, Schiff said his committee would look at allegations that Russian money may have been laundered though Trump’s businesses and that Moscow might have financial leverage over the president.

Nadler’s panel would grapple with any effort to impeach Trump, depending on the outcome of Special Counsel Robert Mueller’s probe into Russian meddling in the 2016 U.S. elections and possible Trump campaign collusion with Moscow.

The panel is expected to look for ways to protect Mueller and his probe from any Trump effort to torpedo the investigation or suppress its findings.