When two Republican members of Congress began formally questioning last week Ivanka Trump’s use of private email for government business, it was seen by people close to the White House as a sign of things to come for the president’s family.

One of the Republicans was Senator Ron Johnson of Wisconsin, chairman of the Senate Homeland Security and Governmental Affairs Committee, which has conducted little oversight of the Trump White House until now.

The other was Representative Trey Gowdy of South Carolina, chairman of the House Oversight Committee, who previously led a two-year investigation into events surrounding the attack on US diplomatic outposts in Benghazi, Libya, focusing relentlessly on the role of Hillary Clinton. His most prominent investigation as chairman has scrutinised alleged anti-Trump political bias within the FBI during its inquiries related to the 2016 presidential campaign.

“That you now have Republicans investigating members of the first family is an indication of the perils ahead” for the Trumps, said Tom Davis, the former House Republican from Virginia who was chairman of the Oversight Committee from 2003 through 2006.

Mr Gowdy, who is retiring from Congress in January, will have little to do with any investigation, and his role in endorsing the inquiry was seen as pro forma. In his place as chairman of the committee will be representative Elijah Cummings, one of the newly empowered House Democrats eager to take on the Trump administration.

Donald Trump Jr is likely to come under scrutiny from the Democrats. Photo: AAP

Likely Democratic targets include not only the president’s personal finances and those of the Trump Organisation, but also the actions taken by his sons Donald Jr and Eric and his son-in-law, Jared Kushner, during the 2016 campaign and its aftermath.

The Oversight and Judiciary committees are likely to focus on any violations of the Constitution’s emoluments clause, which bans payments from foreign governments to federal officeholders, an avenue that will lead to an examination of payments to Trump-held properties and the role of his sons and Mr Kushner. And some investigators may try to question Mr Trump Jr again about a meeting he held with a Kremlin-linked lawyer promising “dirt” about Mrs Clinton.

While some of the areas primed for inquiry — most notably, ties between the Trump campaign, the Trump Organisation and Russia, and possible campaign finance violations — are likely to overlap with investigations by special counsel Robert Mueller and federal prosecutors in New York, Democrats believe they have a broader mandate to question everything from foreign business dealings by Ivanka Trump and the Trump Organisation to the administration of security clearances at the White House, including the one given to Mr Kushner.

Mr Trump has told aides that he believes that Democrats have the potential to appear overly partisan in investigating his family and that voters may be sympathetic to efforts to rebuff them.

Thomas M Reynolds, a former congressman who was the chairman of the National Republican Congressional Committee in 2006, agreed that the incoming House majority would be wise not to meddle excessively in the private affairs of the president’s business and two adult sons.

Ivanka Trump with her father, US President Donald Trump. Photo: Getty

But, he said, “we’re on a thin line here because the president still owns the company”.

Congressional inquiries are treacherous, and can be hard to weather. The president is said to be unprepared for the onslaught he faces, even as the White House Counsel’s Office, which will be led by a new lead counsel, Pat Cipollone, is hiring a raft of lawyers.

Ivanka Trump and her husband have had a veteran Washington lawyer, Abbe D Lowell, working with them for several months. But Mr Trump is famously frugal about hiring personal lawyers, and it is unclear whether he or his adult sons are prepared for how much assistance they will require.

“Politically speaking, this is the achilles’ heel of the administration,” said representative Jamie Raskin, who sits on two of the key investigative panels, referring to the Trump family’s business dealings.

“They have turned the government of the United States into a money-making operation for the president and his family and close friends. That is the exact opposite of our constitutional design.”

– The New York Times