By Susan Cornwell and Patricia Zengerle

WASHINGTON (Reuters) – Back when President Donald Trump was just a New York City real estate developer, he did battle over a Manhattan building project with a local U.S. congressman, whom he criticised as “one of the most egregious hacks in contemporary politics.”

That congressman, Jerrold Nadler, is now a senior member of the U.S. House of Representatives and one of a handful of top Democrats who have tangled with Trump in the past and could soon be in a position to cause serious trouble for him.

If Democrats win a majority in the House in the Nov. 6 congressional elections, Nadler would likely become chairman of the Judiciary Committee. In that post, he could launch investigations of Trump. The committee is also probably where any Trump impeachment effort could begin.

In a multi-front House inquiry of Trump, his business interests and his presidency, Nadler would link arms with Elijah Cummings, who would become head of the House Oversight Committee, and Adam Schiff, who would chair the House Intelligence Committee.

As president, Trump has not dealt with a chamber of Congress under opposition party control, facing few direct challenges from largely cooperative Republicans currently in charge of the House and Senate. That would change if Democrats win the House and start issuing subpoenas that could preoccupy the White House for months.

Opinion polls suggest Democrats could win a majority in the House, but that is far from certain as key races remain competitive days before the election.

“DIVISIVEANDHARMFUL”

Trump’s attack on Nadler was included in one of the future president’s books, “The America We Deserve,” published in 2000.

In February 2017, Trump told a press conference that Cummings had backed out of a meeting with him. Cummings responded that Trump had invented the story.

After the two did meet, Trump told the New York Times in an interview that Cummings told him that he would “go down as one of the great presidents.” Cummings disputed that assertion too.

What he actually told Trump, Cummings told The Baltimore Sun newspaper, was that Trump could be a great president “if he takes steps to truly represent all Americans rather than continuing on the divisive and harmful path he is currently on.”

In an email to Reuters, Cummings said, “If I become chairman, I will not be looking to make headlines. I see my role as defending the truth.”

“SLEAZYADAMSCHIFF”

On Twitter in July 2017, Trump mocked Schiff’s frequent media appearances during the intelligence committee’s probe of Russian meddling in the 2016 U.S. election and possible collusion between Moscow and Trump’s campaign.

Trump’s tweet said, “Sleazy Adam Schiff, the totally biased Congressman looking into ‘Russia,’ spends all of his time on television pushing the Dem loss excuse!”

Schiff defended his appearances, saying the public is interested in the probe. Trump and Russia deny any collusion.

Nadler, Cummings and Schiff plan to make rigorous use of oversight power if the voters award it to them. Schiff said in a recent Washington Post newspaper column that the Democrats “will need to ruthlessly prioritise” their probes.

Michael Steel, a Republican strategist who worked as a spokesman for former House Speaker John Boehner, told Reuters Democrats are likely to overplay their investigative hand.

“There will be irresistible pressure to overreach in their investigations and ultimately impeach the president,” he said.

Nadler, 71, is a hard-nosed, Brooklyn-born attorney. As Judiciary committee chair he would do “the right thing rather than the politically expedient thing,” said Representative Mark Pocan, who co-chairs the Congressional Progressive Caucus to which Nadler belongs.

NO “TORQUEMADA”

Cummings, 67, has been the Oversight committee’s top Democrat since 2011, often squaring off with former Republican Oversight Chairman Darrell Issa, who once memorably cut off Cummings’ microphone while he was speaking.

Congressional aides said Schiff, 58, would work with Republicans if he gets the gavel at the Intelligence Committee, a panel with a bipartisan tradition, but one that predates the Russia probe.

Any Democratic push for impeachment should be the culmination of a transparent, fact-based and fair process, “not the beginning,” said Democratic Representative Gerald Connolly of Virginia.

“You can’t look like Torquemada,” he said, referring to the 15th-century Spanish friar who tortured accused heretics.

But Connolly, an oversight committee member, added, “The public wants to see adult supervision and accountability that is so lacking right now.”

(Additional reporting by Amanda Becker and Mark Hosenball; Editing by Kevin Drawbaugh and Andrea Ricci)