Probably the easiest way to appoint the judges you want is to persuade the public to trust your values and get elected
You can't just 'add justices', Congress has to authorize it. Ignore all the 100 plus federal judges who are mostly minority and let's focus on something unpopular and impossible.
It doesn't matter, Its like trying to win a football game by getting the most first downs The Democrats have a problem getting votes outside urban areas. Their vote is to concentrated.
You said "Probably the easiest way to appoint the judges you want is to persuade the public to trust your values and get elected" Dems did exactly that in 7 of the last 9 presidential elections.