The Washington Times has identified a dozen Democrat senators, including Senators Kerry and Reid, who have flip-flopped on the issue of a troop surge in Iraq. When these senators supported a surge, it seemed to be pure politics: it allowed them to seem strong while criticizing Pres. Bush. They seem to be displaying no principles or insights other than loyalty to party. James Taranto has tracked some of this as they shift from supporting to opposing surges, sometimes in the same speech. (Curiously, MediaMatters seems to think that this absolves the flip-floppers in some way.)
This contrasts with, say, the speech by Sen. Clinton, noted below, where she seems to follow the "principled" liberal approach to foreign policy.
UPDATE: Kevin Drum provides an example of carefully crafted inconsistent impression left by Sen. Edwards on his approach to the Iran issue. UPDATE II: James Taranto has a still more critical look at Sen. Edwards' inconsistencies.