NY Times boils it all down to ideology vs getting things done.
There are two spectra along which to evaluate candidates:
(a) Political: are they left, right or center, and by how much?
(b) Effectiveness: Are they rigidly uncompromising or willing to work with others to get things done?
Often people confuse these as the same thing; all compromisers are centrists, all extremists are rigid, etc. That is a false assumption.