One of the many revelations in former National Security Adviser John Bolton's tell-all book about President Donald Trump's administration, according to Peter Baker of The New York Times, is that Bolton considered the Democrats' impeachment case weak — because they failed to investigate several cases in which Trump tried to exploit international investigations for political gain that might have established a pattern.

"Mr. Bolton ... had nothing for scorn for the House Democrats who impeached Mr. Trump, saying they committed 'impeachment malpractice' by limiting their inquiry to the Ukraine matter and moving too quickly for their own political reasons," said the report. "Instead, he said they should have also looked at how Mr. Trump was willing to intervene in investigations into companies like Turkey’s Halkbank to curry favor with President Recep Tayyip Erdogan of Turkey or China’s ZTE to favor President Xi Jinping."

Bolton was often considered a major potential witness in the impeachment investigation. However, he ultimately did not testify before the House or the trial in the Senate.