I hope not too off topic, but I'm puzzled by shutdowns. Every other country I can think of has a system where if the finance is not agreed, the previous budget just continues. The budget sets the yearly amount for each department and it runs on until another budget changes how much everyone gets. Sometimes a new department gets created, sometimes something is abolished. Everyone gets their salary and services run on.…
THEN rather than Congress passing legislation to say "If nothing else just always stay at past funding levels" Congress instead decided this was a great political tool to whack each other of the head with to negotiate new budgets.
At any point the government could just re-open. The reason shut downs happen is because both the Republicans and Democrats think it's in their favour politically for a shutdown to exist. In this case: Trump thinks he can make the case that we need funding for a border wall (despite controlling all branches of government for part of this shutdown) and that democrats will fold because they don't like dysfunction. Democrats think both that: they can't fold on the border wall because it legitimizes the Republicans using the shutdown to leverage whatever they want, and the border wall is unpopular so a longer shutdown just damages trump more and more.
The only way this resolves is for one group to become so unpopular they fold, or for Trump to shred the constitution and spend the money despite not having the authority (the so called 'State of Emergency' powers)