Blackmun was a sort of stealth candidate, who was nominated after two Nixon conservative appointments were turned down. At this time, the democrats still had their lock on congress, and Nixon being a moderate, not a conservative, threw in the towel. Blackmun's record on the circuit court was mostly about tax issues - not red meat issues that are dealt with today. Although Bush too is a moderate, the republicans control congress, and this was not really a comparable situation.
Breyer was the appointee of Clinton, infamous for his liberal appointments.
Like Blackmun, Kennedy was appointed by a republican (Reagan), who had to deal with a democrat senate, after two conservative nominations had been turned down.
Brennan was a liberal democrat his whole life, and was a recess appointment by eisenhower. According to wikipedia, it was done to woo northeastern catholic democrats, critical voters in the upcoming election, for Eisenhower. This was foolish in the extreme - short term political gain for someone who would rewrite the constitution.
Eisenhower should have known better with Earl Warren. Eisenhower, as a general and president, was an administrative type person, and nominated Warren based on his record as a competent governor of california. Eisenhower apparently didn't interrogate him about his political and constitutional views, although the fact that he was on the ticket with Dewey, an eastern internationalist liberal republican in the 1948 presidential election, should have been a warning.
The idea that justices "mature" on the bench, i.e., become liberals, is a standard mantra of the liberal media (checkout
http://www.amazon.com/gp/product/080...books&v=glance ),
but in fact the reasons republicans have ended up appointing liberals is
1. Inattention, insufficient research.
2. Short term political advantage.
3. Being forced to compromise with a militant democrat senate.
4. Adhering to the old-fashioned gentleman's notion that all that matters is "qualifications".
Bush has a lot on his plate, but none of these should apply if Bush gets a chance at another nomination.