Commentary: Impeachment testimony is also giving Trump a quid pro quo defense

President Trump has offered multiple lines of defense against House Democrats' allegations that he appeared to abuse the power of his office in his dealings with Ukraine's new government. Some are situational and temporary, such as his argument that the process was illegitimate because it hadn't been authorized by a vote of the full House (which it now has been). But one that we are likely to hear throughout is the notion that the president himself did not pressure Ukraine inappropriately to investigate his political rival Joe Biden.

And even as new testimony emerged Tuesday from a Trump ally that shores up the allegations of a quid pro quo,