They’re really targeting California as a whole now. The state that supported the union so much over history. Republicans must really feel jealous that it is the richest state.
Taxes are paid by individuals directly to the federal government. If an individual doesn't pay their federal tax, the federal government goes after that individual. The federal government will take an individual's money right out of their bank account. There's no way for the state to withhold federal payments.
State taxes are filed separately and don't go to the federal government.
I think you need to explain it. Because the vast majority of federal income is from federal income taxes which the state has absolutely no ability to stop. It's between the federal government and the citizen. If the State of California secedes the people still have bank accounts that the federal government will seize.
Also because it's the largest progressive state in size. If they can take down California then they will cheer it on as a major victory. Next up on the hit list the other blue states, Canada and finally Europe.