Frank Bowman III is a law professor at the University of Missouri and author of "High Crimes and Misdemeanors; A History of Impeachment for the Age Of Trump." The opinions expressed in this commentary are those of the author. Read more opinion on CNN.

(CNN) The White House released a rough transcript Wednesday of a July phone call between President Trump and Ukrainian President Volodymyr Zelensky, indicating that the President pressured a foreign leader to gather dirt on a political opponent.

Frank Bowman III

As a result, we now have facts quite distinct from any that have come out about this President before -- and the strongest, or at least most easily explainable, case for impeachment to date.

The allegations at the heart of special counsel Robert Mueller's investigation into Russia's interference in the 2016 election concerned Trump's conduct while he was a candidate for office. There is good authority from the founding era that an effort to corrupt the electoral process ahead of an election might be impeachable. For example, at the 1787 Constitutional Convention, both George Mason and Gouverneur Morris observed that a president who "procured his appointment" by corrupting the electors must be impeachable.

But since impeachment is at its core about a president's misuse of office or suitability to hold it, pre-inauguration conduct at least raises a tricky question. Whatever happened with the Russians during the 2016 election, Trump wasn't then in a position to use the organs of the American state to encourage foreign interference.

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