(Reuters) - At least half a dozen committees of the U.S. Congress are investigating President Donald Trump, who is refusing to cooperate with most of them since the April 18 release of the Mueller report on Russian interference in the 2016 U.S. presidential election, setting up a likely court battle.

The clash between Trump and the Democrats who lead the House of Representatives committees intensified after Trump framed Special Counsel Robert Mueller’s findings as an exoneration, though Mueller neither charged nor exonerated the president.

The report, in the view of Democrats, provided plentiful leads for their further inquiries into ties between Moscow and the 2016 Trump campaign, as well as Trump’s subsequent efforts to stifle the long-running Mueller probe.

Committees are also looking into Trump’s still undisclosed taxes, potential conflicts of interest involving the sprawling business interests he has not divested since taking office, and other aspects of his turbulent presidency.

Congressional subpoenas are being issued and contempt-of-Congress citations are being considered for administration officials who are being advised by Trump to ignore the probes. Civil enforcement actions in the courts may follow.

With the 2020 election campaigns underway and casting both sides’ efforts in an increasingly partisan light, here are the key congressional committees involved.

HOUSE JUDICIARY COMMITTEE

The committee’s Democratic Chairman Jerrold Nadler is an old foe of Trump, going back years to a fight between the two New Yorkers over a large Trump real estate project in Manhattan.

Nadler’s panel has subpoenaed the Justice Department seeking the full, unredacted Mueller report and underlying evidence, as well as former White House counsel Don McGahn to testify in May.

Committee investigators are also focused on contacts Trump’s campaign had with Russia during the 2016 presidential race. Any effort to impeach Trump would likely begin in the committee.

In a book he published in 2000, Trump called Nadler “one of the most egregious hacks in contemporary politics.”

HOUSE OVERSIGHT AND REFORM COMMITTEE

Democratic Chairman Elijah Cummings’ panel in February held 2019’s first public hearing on Trump’s many issues, taking testimony from former Trump attorney Michael Cohen, who is scheduled to report to prison next month.

On April 2, the committee voted to subpoena Carl Kline, a former White House official, over a probe into security clearances granted by the administration.

The White House said it told Kline to ignore the committee’s subpoena. Cummings said the panel will soon vote on whether to hold Kline in contempt of Congress over the matter.

Trump has filed an unprecedented lawsuit attempting to squash a committee subpoena seeking his past financial records from Mazars USA, an accounting firm long used by Trump.

The administration has rebuffed a committee request for an interview with John Gore, an official who was involved in a decision to include a citizenship question in the 2020 census.

Also, the White House has refused a request from the panel for Trump’s top immigration aide Stephen Miller to testify.

HOUSE WAYS AND MEANS COMMITTEE

The House tax committee, led by Democrat Richard Neal, has asked the Treasury Department’s Internal Revenue Service to hand over six years of Trump’s personal and business tax returns.

Unlike presidents in recent decades, Trump has refused to disclose his returns, which committee Democrats want to obtain and review. Committee Republicans argue the committee’s request oversteps its authority.

Treasury Secretary Steven Mnuchin did not meet an April 23 committee deadline for handing over the returns and said that a “final decision” on the request would be made by May 6.

HOUSE INTELLIGENCE COMMITTEE

The committee’s chief, whom Trump has mocked as “sleazy” and “little pencil neck Adam Schiff,” is examining Russian influence in U.S. politics and whether any foreign countries hold leverage over Trump, his family, his business or his associates.

Like other panels, Schiff’s has expressed an interest in having Mueller testify about his findings.

SENATE INTELLIGENCE COMMITTEE

Republican Chairman Mark Warner’s committee is also looking into Russia’s role in influencing U.S. elections. The committee could release its findings later this year.

In late March, Trump adviser Jared Kushner, the president’s son-in-law, made a second appearance before the panel, according to congressional sources. Topics discussed in the closed-door sessions were not made public.

HOUSE FINANCIAL SERVICES COMMITTEE

Democratic Chairwoman Maxine Waters, whom Trump has also frequently mocked, is leading a probe into Trump’s ties with Deutsche Bank AG, one of the world’s largest financial institutions, as well as potential Russian money laundering through the bank. The committee oversees the financial services industry including banks.

Waters has said the House should impeach Trump.