Mebbe 60% as high as it will go because the bedrock red rock-solid base will never agree. I do not know what percent that is. Anywhere from 35% to 40%? Who knows? Who cares? Whassup?
The single most potent force that would determine whether Republicans hold their support for the President will be the public consensus for or against removal from office.
If one is to believe polls, this trend is not positive for Trump at present.