This is my read on the situation. Mitt Romney and Lisa Murkowski voted for witnesses because they want more evidence so that they can justify their vote for convicting Trump. Susan Collins may be undecided but definitely wants more witnesses. Lindsey Graham sees this as a political opportunity to showboat and convince voters to reelect him. Graham sees this as another Brett Kavanaugh - Christine Blase Ford hearing.
My take on the whole of this....is if you want witnesses, they should have been called BEFORE they impeached him on a whim.