Republicans on the Hill are taking to heart the old adage, "To be forewarned is to be forearmed," when it comes to what they might expect from Democrats if they take over either chamber in November.

GOP lawmakers have been circulating a list of more than 100 issues Democrats might investigate if they achieve a majority and take over the chairmanship of committees and acquire the power of subpoena.

TPM:

The outlet published a list, which it said had circulated in spreadsheet form "through Republican circles on and off Capitol Hill – including at least one leadership office," detailing the subjects on which Democrats have called for investigations since Trump's inauguration.

With the majority in either chamber, Democrats would have the power, in the form of committee chairmanships, to pursue their investigative interests.  Axios' Jonathan Swan said he was told that the spreadsheet originated in a "senior House Republican'"s [sic] office.

Axios reported the spreadsheet catalogs "more than 100 formal requests from House Democrats this Congress."

"Some of the probes it predicts," Axios reported, are the following:

• President Trump's tax returns
• Trump family businesses – and whether they comply with the Constitution's emoluments clause, including the Chinese trademark grant to the Trump Organization
• Trump's dealings with Russia, including the president's preparation for his meeting with Vladimir Putin
• The payment to Stephanie Clifford – a.k.a. Stormy Daniels
• James Comey's firing
• Trump's firing of U.S. attorneys
• Trump's proposed transgender ban for the military
• Treasury Secretary Steven Mnuchin's business dealings
• White House staff's personal email use
• Cabinet secretary travel, office expenses, and other misused perks
• Discussion of classified information at Mar-a-Lago
• Jared Kushner's ethics law compliance
• Dismissal of members of the EPA board of scientific counselors
• The travel ban
• Family separation policy
• Hurricane response in Puerto Rico
• Election security and hacking attempts
• White House security clearance

There are actually a lot more topics Democrats will investigate.  From the looks of things, about half the White House will eventually be under subpoena.

Some of those topics are ridiculous.  Others may hit paydirt.  Republicans can expect daily headlines of "revelations" that reflect badly on Trump and the GOP.

What kind of impact would these investigations have on the 2020 race?  In 2012, Barack Obama and his administration were facing at least a dozen serious inquiries, including several involving his secretary of state, Hillary Clinton, and a few that involved impeachable offenses.  Obama still won by a comfortable margin.

The lesson is that a relatively small number of voters care about congressional investigations and don't follow them closely enough to be influenced by them.  Today, even a report from Robert Mueller that recommended indicting or impeaching Trump would be seen as the partisan exercise it is.  Its ultimate political impact would be negligible.  Most voters have already made up their minds about Trump, and unless there's clear evidence that Trump personally conspired with Russians to win the election, the damage to his re-election prospects will be minimal. 

Trump will win or lose in 2020 based on how many Republicans turn out to vote for him, not how many crooks and knaves he has working for him.