Ron Johnson qualifies as impeachment witness. For the Democrats.

Oh, RoJo: You weren't supposed to help make the quid pro quo case, but thank you for the stumble, which the Journal Sentinel reports this way: 

Ron Johnson says he was blocked by President Trump from telling Ukraine foreign aid was coming

With his comments Friday, Johnson made clear that he was aware of allegations Trump was withholding aid to Ukraine for political reasons weeks before the public knew.  

And, wow, is Johnson having a bad day:

Johnson on Friday also sought to walk back comments he made Thursday about whether the president acted properly by calling on a foreign government to investigate Joe Biden, the former vice president who is running for president....That's in contrast to comments Johnson made Thursday to reporters in Wisconsin.

You know, with walking-back friends like these, Trump doesn't need any enemies.