Nixon was pardoned without being charged.
Perhaps it could have been challenged in court. In any case, a presidential pardon won't absolve him of anything at the state level. The tax investigation that I think will be extremely revealing about his illegal money laundering empire is a NY state concern.
As of sept. 26, 2019,
this article lists 30 investigations underway. 10 of them could be wiped out by Presidential pardon. Congressional investigations could continue but he might not be charged if there were a pardon. His kids would still be fair game.
12 - CONGRESSIONAL INVESTIGATIONS
10 - FEDERAL CRIMINAL INVESTIGATIONS
8 - STATE AND LOCAL INVESTIGATIONS
Congressional Investigations
In the months since Democrats took control of the House, several committees have opened inquiries that could turn up politically damaging or embarrassing material or lead to impeachment proceedings.
Select an investigation to see more.
1. Possible abuse of power by using foreign policy for political ends
2. Potential foreign influence over Trump and possible attempts to obstruct justice
3. Possible role of Trump and others in concealing hush money payments
4. Possible obstruction of justice and abuse of power by Trump and his administration
5. Possible abuses of the White House security clearance process
6. Whether Trump misrepresented his net worth House Oversight and Reform Committee
7.Alleged use of private messaging by White House officials
8. Trump’s tax returns
9. Trump’s communications with Putin
10. Possible money laundering
11. Russian interference in the 2016 election
12. Proposed U.S. nuclear venture in Saudi Arabia
Federal Criminal Investigations
Federal prosecutors are pursuing more than a dozen criminal investigations that
grew out of the work of Robert S. Mueller III, the special counsel. These are the ones we know about.
13. Trump inaugural committee
14. Trump inaugural committee donations / committee chairman’s ties to Middle East
15. Business and political dealings of top fund-raiser for Trump’s campaign and inauguration
16. Possible role of Trump and others in concealing hush money payments
17. Whether Trump’s lawyers offered presidential pardon to Cohen
18. Allegations of inflated insurance claims
19. Pending prosecution of Roger J. Stone Jr.
20. Possible lobbying violations by firms recruited by former Trump campaign chairman
21. Pending prosecution of former Manafort associate
22. Bank officer who sought Trump administration job
State and Local Investigations
Authorities in New York, New Jersey and Washington, D.C., are also examining Mr. Trump, his businesses and associates through various — mostly civil — investigations.
23. Trump Organization insurance practices
24. Contributions to Trump inaugural committee
25. Role of Trump’s children and businesses in Trump’s inauguration
26. Pending criminal prosecution of Manafort on state mortgage fraud charges
27. Allegations of misused charitable assets, self-dealing and campaign finance violations by the Trump Foundation
28. Allegations that the Trump Organization inflated financial assets
29. Trump family’s tax schemes
30. Whether Trump and his family underpaid taxes