It is to Trump's advantage for the Democrats to consolidate all of the investigations under the one impeachment umbrella. That way, he'd have one enemy, one foil and he has proven to be an expert at that kind of battle. He is not as adept at fighting on multiple fronts.
...
T]hey don't want Schiff and the House Intelligence Committee rooting around in Trump's foreign entanglements while, at the same time, Ways and Means obtains and analyzes his tax returns while Waters and her Financial Services Committee are going through his banking records and calling in Deutsche Bank executives to testify about them and Cummings and the Oversight Committee are hauling administration officials in to explain themselves ...

Instead of dealing with several House investigations, Trump's people want to focus like a laser beam only on the Judiciary Committee's impeachment inquiry and to narrow that focus on the Mueller Report so that the Articles of Impeachment are limited to those specific issues, which are already known to the public, who haven't been swayed in great numbers by it. They want and need to make the impeachment inquiry the boogeyman, instead of dealing with several different investigations on several different fronts.

They want nothing more than for the Democrats to rush in before they've completed their other investigations and impeach Trump on a fairly limited scope of wrongdoing and they want them to do it soon so that the Senate can acquit by the end of the summer and then leave Trump more than a year to refocus the argument away from impeachment and leave him plenty of time to throw out 400 or so new outrageous distractions and make his impeachment an irrelevant distant memory come November 2020.

https://www.democraticunderground.com/?com=view_post&forum=1002&pid=12087849

(Courtesy Chowder66)
https://www.democraticunderground.com/100212157411

JUDICIARY: Chairman Jerrold Nadler, D-N.Y.

Oversight of the administration's family separation policy
Former acting Attorney General Matthew Whitaker’s appointment, his involvement in the Mueller investigation, and his conversations with Trump and involvement with World Patent Marketing
Voting rights and Department of Justice actions on voter ID, census cases
Easing of sanctions on companies linked to Russian oligarch Oleg Deripaska
Trump's national emergency declaration
The president's "threats to the rule of law," covering three main areas:
Obstruction of justice, including the possibility of interference by Trump and others in a number of criminal investigations and other official proceedings, as well as the alleged cover-up of violations of the law;
Public corruption, including potential violations of the Emoluments Clause of the U.S. Constitution, conspiracy to violate federal campaign and financial reporting laws, and other criminal misuses of official positions for personal gain;
Abuses of power, including attacks on the press, the judiciary, and law enforcement agencies; misuse of the pardon power and other presidential authorities; and attempts to misuse the power of the office of the presidency.
Trump's interference in Time Warner merger
Threats to relocate migrants to sanctuary cities
Reports that the president said he would pardon acting Department of Homeland Security Secretary Kevin McAleenan if he illegally closed the southern border to migrants
Firings of senior leadership at DHS
The administration's decision to stop defending the Affordable Care Act in court

OVERSIGHT AND REFORM: Chairman Elijah Cummings, D-Md.

Oversight of the Trump administration’s family separation policy
Acting Attorney General Matthew Whitaker's involvement with World Patent Marketing
Reports that the Citizenship and Immigration Services Ombudsman was failing failing to carry out statutory duties to help those applying for legal immigration programs
White House security clearances
Inclusion of a citizenship question on the 2020 census
Easing of sanctions on companies linked to Russian oligarch Oleg Deripaska
Delayed back pay for federal workers impacted by the government shutdown
Michael Cohen hush-money payments
Education Secretary Betsy DeVos' efforts to replace her agency's acting inspector general
Transfer of nuclear technology to Saudi Arabia
Child separation actions at DOJ, DHS and Health and Human Services
Communications between Russian President Vladimir Putin and Trump
Michael Cohen's claims that Trump was improperly inflating financial statements
Interior Secretary David Bernhardt's schedules
Trump's threats to relocate migrants to sanctuary cities
Use of private email accounts by Jared Kushner, Ivanka Trump and other White House officials, and use of messaging apps like WhatsApp
Gag orders on White House staff
Title X gag rule regulatory review process
Potential lobbying conflicts of interest involving Environmental Protection Agency head Andrew Wheeler
Interior Department's handling of FOIA requests
Abandoning plan to move FBI HQ building from Washington to suburban location
Firings of senior leadership at DHS
Trump Administration’s response to hurricanes in Puerto Rico and U.S. Virgin Islands
Trump Administration’s decision to stop defending ACA

INTELLIGENCE: Chairman Adam Schiff, D-Calif.

Russia investigation, including the scope and scale of the Russian government's operations to influence the U.S. political process, and the U.S. government's response, the extent of any links and/or coordination between the Russian government, or related foreign actors, and individuals associated with Trump's campaign, transition, administration or business interests, whether any foreign actor has sought to compromise or holds leverage, financial or otherwise, over Trump, his family, his business, or his associates; whether Trump, his family, or his associates are or were at any time at heightened risk of, or vulnerable to, foreign exploitation; and whether any actors — foreign or domestic — sought or are seeking to impede, obstruct, and/or mislead authorized investigations into these matters
Whether lawyers for Trump and his family obstructed committee's Russia probe
Trump's personal finances, including loans from Deutsche Bank
Use of intelligence to justify building a wall at the southern border
Easing of sanctions on companies linked to Russian oligarch Oleg Deripaska
Communications between Putin and Trump

WAYS AND MEANS: Chairman Richard Neal, D-Mass.

Easing of sanctions on companies linked to Russian oligarch Oleg Deripaska
Trump administration's use of user fees generated by the Affordable Care Act
Rule on short-term insurance plans
Trump administration’s decision to stop defending ACA
The president's personal and business tax returns

FOREIGN AFFAIRS: Chairman Eliot Engel, D-N.Y.

Communications between Putin and Trump
Trump administration's failure to produce Russian sanctions report

FINANCIAL SERVICES: Chairwoman Maxine Waters, D-Calif.

Easing of sanctions on companies linked to Russian oligarch Oleg Deripaska
Trump's personal finances, including loans from Deutsche Bank
Trump administration's failure to produce Russian sanctions report
Reported ransom demand from North Korean government related to Otto Warmbier

https://www.nbcnews.com/politics/donald-trump/house-investigations-trump-his-administration-full-list-n1010131

I’m not impressed with far-left Democrats claiming they were leaders on impeachment by seeking President Trump’s ouster two years ago. It would have been foolhardy until now to progress to impeachment.

A fact pattern as complicated as the Trump campaign’s solicitation of Russian help and Trump’s attempt to cover it up was destined to lose the public’s attention. It took special counsel Robert S. Mueller III 22 months and 448 pages to explain it. Moreover, in that set of circumstances the Trump-appointed attorney general could get his hands on it first, massage the facts and then instruct executive branch witnesses not to cooperate. Congress did not have the right facts nor the right powers to dislodge the truth in a compelling fashion. The public remained staunchly opposed to impeachment for Russia-related issues.

House Speaker Nancy Pelosi (D-Calif.) can read the polls and knows her members. Moreover, she knows a thing or two about public sentiment and how to sway it. Holding off on impeachment until the Ukraine scandal popped up gave her several advantages.
...
A skilled leader doesn’t go plunging into the abyss of impeachment without her party, the public and a concise narrative all lined up. She learns from past errors (e.g., don’t rush to court to compel testimony, a process that takes months, and don’t let members conduct factual inquiries at hearings) and adjusts her strategy accordingly. One can see just how skillful Pelosi has been by the lack of a coherent response from Republicans. By picking the right fight at the right time — and withstanding outside pressure to act precipitously — Pelosi has positioned her members to make the best possible case against Trump while defending their majority. In retrospect, it certainly is fortunate her members didn’t push her out of the way in favor of a novice leader.

https://www.washingtonpost.com/opinions/2019/09/25/pelosi-was-right-wait/