No far-left state is going to split in “half” — ever.
Why would Democrats concede to going from a situation where a state has 2 Democrat Senators, to having the same area on the map suddenly have 2 Democrat Senators and 2 Republican Senators?
Never happen.
A state would have to split into at least 3 parts (2 of which favor Democrats) or it will never have the slightest chance of being allowed.
There would be no change to senators since Eastern Oregon would be joining Idaho. Oregon would benefit since Eastern Oregon only draws revenue and provides Republicans to the state legislature.
A new state needs to be created. Take the existing State of Jefferson proposal and add Eastern Oregon and Eastern Washington.
Actually, we need about fifty new states for more accurate representation. Every major metro area needs to be expelled into statehood.