Sullivan is not a 'liberal' in the modern sense. His positions are mostly congruent to that of liberals on social issues, and on some but by no means all 'liberty' issues (individual rights vs. government power.) However, Sullivan is implacably opposed to socialism, to the New Deal and to the Great Society--more so than most Republicans. Were he elected President, most Federal spending other than for Defense would be stopped by Executive Order on Day 1 of his Presidency (he would declare it Unconstitutional.) Or to say the same thing in far fewer words: He's a Libertarian.
Fair enough.