Bolton says in his new book that the House in its impeachment inquiry should have investigated Trump not just on Ukraine but for a variety of instances when he sought to intervene in law enforcement matters for political reasons. https://www.nytimes.com/2020/06/17/us/politics/bolton-book-trump-impeached.html

During Trump’s 2018 meeting with Kim Jong-un, Pompeo slipped Bolton a note disparaging the president, saying, “He is so full of shit.” Pompeo later said the North Korea diplomacy had
"zero probability of success."

Trump didn’t seem to know that Britain was a nuclear power and asked if Finland were part of Russia, Bolton writes. Intelligence briefings were a waste of time “since much of the time was spent listening to Trump, rather than Trump listening to the briefers.”

Trump directly asked China’s Xi to buy agricultural products to help him win farm states in 2020, Bolton writes. Trump was “pleading with Xi to ensure he’d win. He stressed the importance of farmers, and increased Chinese purchases of soybeans and wheat in the electoral outcome.”

Trump talked about intervening in criminal cases like ZTE and Halkbank "to, in effect, give personal favors to dictators he liked," Bolton writes. "The pattern looked like obstruction of justice as a way of life, which we couldn’t accept."

Bolton confirms previous @maggieNYT @nytmike report on Trump linking security aid for Ukraine to his desire for investigations into Democrats. But he says Democrats should have looked at the Halkbank and ZTE matters, among others, to build a broader case.

Had they done so, he writes, "there might have been a greater chance to persuade others that ‘high crimes and misdemeanors’ had been perpetrated."