The burden of proof to remove is on the prosecution. If you are a Senator that voted for more witnesses, you essentially admitted that there is not yet enough evidence for removal, i.e., you need to see more evidence before you vote.
How then, do you turn around and vote to convict anyway without seeing the additional evidence? The whole thing is ridiculous.
Someone in the media needs to straight up ask Romney this question: "You voted for more witnesses, meaning you felt that there was insufficient evidence to remove (why else the need for more witnesses?) Why then, are you voting to remove WITHOUT THAT EVIDENCE?"
Truly excellent point. Damn mitt. I voted for that man to be President once, and disappointed that he lost. Now I just want to throw down with anyone that defends him.