Firing Mueller is a booby trap. Why do you want Trump to fall into it?
1) Democrats are going to try to impeach him either way, which won’t succeed in the Senate and if anything may assist him in his reelection bid.
2) He’s giving the Democrats the opportunity to save Mueller’s job. He could even offer them a proviso that he can’t fire Mueller (unenforceable/unconstitutional anyway) in exchange for wall funding.
3) The last long government shutdown only ended because of the debt ceiling. The longer the shutdown, the more it hurts Democrats since it shows how meaningless shutdowns really are. The more often they happen, the less R’s will be afraid of them. It no longer remains leverage for Democrats if you learn to become indifferent about the idea of shutdowns.
4) I can see Democrats eventually telling their deranged base that they need to give Trump his wall money in order to reopen the government and begin impeachment proceedings, etc.