Judging Impeachment: A Third Oath and a Criterion for Judgment--or "What of the Shoe Was on the Other Foot?"

I'm been thinking about how we could set a standard to allow Senators to return an appropriate judgment at the conclusion of the current impeachment trial. To begin, let's start with the oath that each senator takes when beginning their term of office. (See Below)

At the beginning of the current trial, each senator took this oath as well.
(See below)

Now, perhaps before returning a decision, each senator should take another oath. However, the oath would not be the same for each senator. Each senator would take the following oath before announcing the senator's judgment:

"I swear (or affirm) that the decision I make today is the same decision I would make if the president in question would have been Barack Obama, Bill Clinton, or any other Democrat. I have not been moved by partisan favor or any motive other than to uphold and defend the Constitution of the United States of America, so help me God."

So New York Senators Chuck Schumer and Kristin Gillibrand should take it as well as Senator Chuck Grassley and Senator Joni Ernst. All of them. And then the voters will determine if each one upheld the oath.

Of course, this isn't going to happen, but is it a bad idea? Moreover, isn't this the criteria--regardless of any oath--by which each of the 100 senators should be making her or his decision?

I welcome suggestions or rebuttals.