Donald Trump cannot provide exculpatory witnesses - he must provide *under oath* testimonies

Echo opinion letter published in the Florida Sun Sentinel - Donald Trump cannot exculptate himself because there are zero witnesses who will agree to lie for him when "under oath".  On the other hand, witnesses who have put their professional reputations at risk did testify under oath to provide proof of Donald Trump's obstruction of Congress and abuse of power, as charged in the Articles of Impeachment.

Where are the Trump exculpatory witnesses who are willing to provide testimony under oath? IOW, the exculpatory witnesses do not exist.  

Echo opinion letter from Florida:

Dr. Fiona Hill, the former National Security Council, while under oath, corroborated the U.S. Intelligence Community and those who testified before her. She said she refuses to legitimize the conspiracy theory she called a false narrative, fueled by Russian propaganda, that Ukraine interfered in our election in 2016, and warned of Russian efforts to “weaponize” U.S. politics. That’s really scary to me.

The Mueller report is clear on this point, so Donald Trump knows better: The U.S. intelligence community has concluded that the Russian government was behind an orchestrated campaign to interfere in the 2016 US presidential election and sought to help Donald Trump win the White House. The Mueller investigation did indict 26 Russian nationals and three Russian companies.

David Holmes testified, under oath as well, that the president didn’t care about the corruption in Ukraine, he just cared about getting dirt on the Bidens. That is illegal and the America public needs to know that Donald Trump broke the law, even if he is not impeached. Maybe future presidents will think twice before they break the law.  

From Ann O’Leary, Lauderhill, Florida