Here is a major flaw in your understanding of how SCOTUS works. Justices are under no obligation to make decisions based on what the law was designed to do. Justices often make decisions based on the text of the law, and if the text does not match what the law was designed to do, they expect Congress to remedy their poor writing skills.
No. Presidents are appointing judges for their judicial philosophy, previous rulings, race, gender, thoughts on Roe v. Wade, thoughts on the Second Amendment, what state they come from, what they promised voters, whether or not they will get past the Senate, and a host of other reasons too long to list, that changes on a regular basis.
Presidents really don't care if the appointees are voting for Democrats or Republicans.
This is a much more nuanced process than you seem to think it is.