In yet another demonstration of the changed tone he debuted in his election-night victory speech, President Barack Obama, in his first press conference since winning re-election, both challenged his opponents to act in the interest of the overwhelming majority of Americans, and castigated two high-profile senators for launching a media campaign against the possible nomination of U.N. Ambassador Susan Rice to head the State Department when Hillary Clinton leaves the post. He also dinged his former rival for the presidency, Mitt Romney, with faint praise.