Congressional democrats have begun inquiries into impeachment of President Trump allegedly because Trump “tried to pressure” the Ukrainians into investigating possible corruption by former VP Joe Biden and his son. I have not heard reference of this treaty from the democrats or the “mainstream” press.
However, Trump was entirely within his legal purview according to a treaty signed into law during the Clinton administration: Mutual Legal Assistance in Criminal Matters.
The original treaty was signed in Kiev on July 22, 1998. Clinton transmitted the treaty to the Senate on October 19, 1999, and it was ratified by the Senate on October 18, 2000. The following link shows Clinton’s Letter of Transmittal, Clinton’s Letter of Submittal in which he summarizes the main points. This is follow by the full text of the treaty.
Treaty: https://www.congress.gov/106/cdoc/tdoc16/CDOC-106tdoc16.pdf
Senate confirmation: https://www.congress.gov/treaty-document/106th-congress/16/document-text