Presented the gift of two Supreme Court seats to fill in his first 15 months in office, Barack Obama appointed liberals Sonia Sotomayor and Elena Kagan. Given their relative youth--Sotomayor was 55 when appointed, and Kagan only 50--Obama likely cemented their seats on the left for the next two or three decades.
In his second term, President Obama could, depending on which vacancies arise, push the Court further leftward and engender a new era of aggressive liberal judicial activism. At the very least, he is likely to entrench another seat on the left.
As a backdrop for assessing the damage that Obama might inflict, let's consider the current state of the Court along two dimensions: ideology and age.
In rough ideological terms, the Court currently consists of four judicial conservatives (John Roberts, the chief justice--in my judgment, the Obamacare ruling provides no basis for reclassifying his general position on the ideological spectrum--along with Antonin Scalia, Clarence Thomas, and Samuel Alito) and four liberals (Ruth Bader Ginsburg, Stephen Breyer, Sotomayor, and Kagan). Then there's the swing justice, Anthony Kennedy, who has swung with the liberals in some huge cases and with the conservatives in others. For example, Kennedy provided the critical fifth vote in 1992 to retain Roe v. Wade and in 2003 to invent a constitutional right to homosexual activity, yet he also joined (and presumably authored) the majority opinion in Bush v. Gore and wrote the Citizens United ruling against campaign-finance restrictions.
As for age, the nine justices can be grouped into two cohorts. In the older cohort are Ginsburg (79), Scalia (76), Kennedy (76), and Breyer (74)--two liberals, a conservative, and Kennedy. In the younger cohort, the conservatives--Thomas (64), Alito (62), and Roberts (57)--currently have a three-to-two edge over the liberals--Sotomayor, now 58, and Kagan, the youngster at 52. (It's striking that Thomas, who has been on the Court for more than two decades, is only two years older than Alito.)
Combining these dimensions, we see that if Obama is able, say, to replace both Ginsburg and either Scalia or Kennedy with liberals in their 50s, he will establish a liberal majority on the so-called Roberts Court and create a four-to-three edge for liberals among the younger justices. If he is somehow able to replace Ginsburg, Scalia, and Kennedy with young liberals, he will likely ensure two or three decades of liberal dominance of the Court. . . .