• "He knows what I think about leaders. What happens if he reveals how I feel about another leader and it's not positive ... it would make the job a lot harder," Trump said.
  • Bolton is a firsthand witness to the president's efforts to strongarm Ukraine into pursuing investigations that would be politically beneficial to him while withholding military aid and a White House meeting for Ukraine's president.
  • If the Senate allows Bolton to testify, he would be the most high-profile witness against the president to date.
  • Visit Business Insider's homepage for more stories .

President Donald Trump said on Wednesday that he's opposed to the former national security adviser, John Bolton, testifying in his impeachment trial because "it's a national security problem."

"He knows some of my thoughts," Trump told reporters . "He knows what I think about leaders. What happens if he reveals how I feel about another leader and it's not positive ... it would make the job a lot harder."

Trump's statement, however, underscores why Democrats believe Bolton's testimony is crucial: he "knows some of" Trump's thoughts.

The president's comments came just hours before opening arguments are set to kick off in his Senate trial only the third in US history. Trump was impeached last month for abuse of power and obstruction of Congress.

Bolton announced this month that he's willing to testify in the impeachment trial and is a firsthand witness to the president's efforts to strongarm Ukraine into pursuing investigations that would be politically beneficial to him while withholding vital military aid and a White House meeting that Ukrainian President Volodymyr Zelensky desperately sought.

The former national security adviser left his role in the Trump administration last summer but was privy to several key events at the center of the impeachment inquiry, according to his lawyer and public testimony from other current and former government officials.

The White House directed all executive branch officials not to comply with congressional subpoenas for testimony last year. While more than a dozen lower-level officials refused to follow the White House's directive, all senior officials including Bolton, Secretary of State Mike Pompeo, the acting White House chief of staff Mick Mulvaney, and more followed the White House's order.

Bolton, if he testifies, could be the president's worst nightmare. As the former national security adviser, he would be the highest-profile witness to testify against Trump and one who held frequent meetings with him.

  • Bolton attended a July 10 White House policy meeting between senior US and Ukrainian officials. Gordon Sondland, the US's ambassador to the European Union, hijacked the meeting when he told the Ukrainians that Trump wanted a "deliverable" specifically, politically motivated investigations in exchange for a White House meeting.
  • Bolton immediately cut the meeting short at that point and informed Fiona Hill, who at the time was the National Security Council's senior director in charge of Russian and Eurasian affairs, to "tell the lawyers" what had happened.
  • Hill said in her testimony that Bolton ordered her to tell John Eisenberg, the NSC's chief counsel, that he was not part of "whatever drug deal" Sondland and Mick Mulvaney, the acting White House chief of staff, were "cooking up" in Ukraine.
  • Bolton was staunchly opposed to Trump making the infamous July 25 phone call to Zelensky.
  • Hill and other witnesses testified that Bolton was against the phone call because he feared the president would use it to air his personal grievances to Zelensky, which is exactly what ended up happening.
  • The former national security adviser described Rudy Giuliani, Trump's personal lawyer who spearheaded what witnesses have said was the "irregular channel" of foreign policy in Ukraine, as a " hand grenade ." Bolton was also opposed to the smear campaign Giuliani and Trump carried out against Marie Yovanovitch , the US's ambassador to Ukraine.
  • Asked why Bolton described Giuliani as a "hand grenade," Hill told Congress that the former New York mayor was "clearly pushing forward" issues that would "probably come back to haunt us," adding, "That's where we are today."
  • Bolton's lawyer, Chuck Cooper, dropped a tantalizing hint in a letter to Congress indicating that Bolton knows even more than what's already been revealed.
  • Bolton "was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far," Cooper wrote.
  • Bolton has receipts.
  • Current and former senior administration officials told the news website Axios that people in Trump's orbit were terrified of what Bolton may have documented and what he might divulge.
  • According to Axios' sources, Bolton is a prolific note-taker and likely has more details than any witness in the impeachment inquiry so far about Trump's shadow campaign in Ukraine.
  • "Bolton was a voracious note-taker, in every meeting," one source who attended several meetings with the former national security adviser told Axios. Apparently, Axios reported, while others sat and listened in meetings with the president, Bolton "distinguished himself by filling legal pads with contemporaneous notes on what was said in the room."

NOW WATCH: A law professor weighs in on how Trump could beat impeachment

See Also:

SEE ALSO: John Bolton just became Trump and the GOP's worst nightmare