In this relatively narrow sense, it’s hard to portray Mr. Obama as a triangulator. Aside from one impromptu soliloquy at the end of a news conference last week, when he appeared to be venting his genuine frustration with the left over the tax agreement, he hasn’t sought to highlight his disagreement with liberals to burnish his own credentials as a reformer…

But of course, triangulation is no longer limited to such a narrow definition. During the Bush years, the new self-described progressives inside the Democratic Party became increasingly furious with the tendency of their politicians to cooperate with Republicans and acknowledge conservative arguments, rather than hold firm to a series of liberal litmus tests. Ultimately, triangulation became a broader term for compromise generally, even if the compromise in question went some way toward furthering progressive goals.

“Again and again, we have Democratic presidents who say, ‘Don’t make the perfect the enemy of the better,’ and ‘This is the best I can do,’ ” says Robert Reich, the liberal economist and former labor secretary under Mr. Clinton. “And over and over we have Republican presidents who say, ‘I am going to hold out for my principles.’ ”