Obama campaigned in 2008 as a Brzezinsky style realist but governed more or less like a liberal interventionist. George W. Bush promised a realist foreign policy as candidate in 2000 but governed like a neocon.
The liberal interventionists and neocons are called Idealists, sometimes Wilsonian Idealists and their idealism manifests as humanitarianism, nation building, and spreading democracy. So it is really the Idealists versus the Realists.
As for Obama, he did follow the realists in 2009 and 2010, but when he began his campaign for re-election in 2011 he shifted to the liberal interventionists. He didn't want to get Carterized. And after his re-election he is back to realist.
For example: He hired George Mitchell(realist) as special envoy to push on Israel regarding the Palestinians. And when Obama began his re-election campaign in 2011, he got rid of Mitchell and stopped pushing on Israel, but not totally. Obama appointed Dan Shapiro(realist) as ambassador to work around Bibi. Then, after re-election, he put Kerry(realist) in as SoS who is pushing very hard on Israel.
That was probably a mistake. It doesn't make any difference how hard Kerry or anybody else pushes on Israel, Israel ain't gonna make a deal with the Palestinians.
By moving Kerry from chairman of the Senate Foreign Relations Committee to SoS, Obama lost control of the committee. Liberal Interventionist dem Menendez now controls the committee and Realist republican Corker is very weak.