Actually, no: the 18 minute gap in the White House tapes was never actually linked to President Nixon - his secretary, Rose Mary Woods, allegedly made some mistake with the tape that was never solved.
The main fact was that once the White House taping system was disclosed, President Nixon refused to destroy any of the tapes as his advisors had recommended. There was no "obstruction of justice".
If you really want to see Obstruction of Justice, try the IRS' wholesale destruction of computer hard drives and files - against congressional instructions - during Obama's reign - and Hillary's destruction of all evidence during her highly illegal use of a personal computer and server to transmit classified information.
All I remember is the missing 18 minutes of tape. Sadly all he had to do was not try to cover up. I do believe this country owes an apology to Nixon for what they let Obama get away with.