Any breakthroughs in Korea won’t act as a get-out-of-jail-free card for Trump’s corruption. And remember, there haven’t really been any big breakthroughs yet.
Nixon isn’t best remembered as the president who began détente with the USSR or who opened relations with China, he’s best remembered for Watergate, and for being compelled to resign in disgrace over it.
It bears mentioning that despite the parallels between the two leaders, Nixon was a much more thoughtful and cautious leader than Trump. Nixon didn’t run around ruining international goodwill and the trustworthiness of the USA by tearing up multiple international agreements (Paris, NAFTA, TPP, Iran) like Trump has.
It also bears mentioning that Trump’s corruption possibly rises to the level of treason, and thus is potentially vastly more serious than Nixon’s.
Finally, Nixon had a record of working across the partisan aisles and proposing politically moderate legislation that both parties could back. Nixon won landslide victories due to his ability to appeal to the votes of normally Democratic voters. Trump is an abrasive, rank partisan with historically low approval ratings for a president.
In trying to use foreign policy to distract from domestic scandal, Trump is playing from a weaker hand with a strategy that has proven a failure in the past.