Quid pro quo, means this for that. I'll send you the military aid, once you announce an investigation, a "favor." Trump asked for it, because he directly benefits from it. It helps his reelection campaign if his opponent is under investigation. Hopefully we can all see that. Quid pro quo isn't illegal in and of itself, the US does it all the time. But what Trump was asking interferes in the US's political process. SO forget about quid pro quo, Trump solicited help from a foreign nation. He explicitly did it, requesting that Zelensky look into the Bidens and the debunked conspiracy theory that Ukraine interfered in the 2016 election. It is accepted by the entire intelligence community that Russia was behind it. SO regardless of quid pro quo, it is illegal for a candidate or campaign to "solicit" help from a foreign gov't, whether it's money or something else of value. Bribery is also illegal, and grounds for impeachment. "specific intent to give or receive something of value (Biden investigation) in exchange for an official act (meeting at WH, military aide).
So then Biden should expect the police at his door any minute? Trump didn't do anything of the sort.
