Bernie Sanders has set a high goal for himself. He wants to unleash nothing less than a political revolution in America that overthrows the power of big money. In pursuit of this goal, he’s launched a highly energetic and lofty grassroots movement. But it could be that as a candidate he’s a bit too lofty for his own good.

He is clearly more comfortable debating ideas than launching personal attacks. Throughout the second Democratic presidential primary debate, he performed an awkward dance where he drew a sharp contrast between himself and front-runner Hillary Clinton, but for the most part pulled back from landing a direct hit. Time and again, he tried to present his differences with Clinton in abstract terms, often refusing to name her explicitly as being at fault. For whatever reason, Sanders lacks the killer instinct you need to be a politician at the highest level.

The examples of Sanders shying away from or even muffling criticism of Hillary Clinton are worth examining in detail. Consider how Sanders tried to draw a distinction between himself and Clinton on foreign policy:

SANDERS: I agree with much of what the secretary and the governor have said. But let me have one area of disagreement with the secretary. I think she said something like the bulk of the responsibility is not ours. Well, in fact, I would argue that the disastrous invasion of Iraq, something that I strongly opposed, has unraveled the region completely and led to the rise of al Qaeda and to ISIS.

This is a strong argument about perhaps the most grievous mistake in Hillary Clinton’s political career. Clinton was visibly gulping when the issue of her Iraq vote was brought up.

But note how qualified it is. Sanders starts by noting broad areas of agreement, so the Iraq vote becomes a mistake (which Clinton acknowledged), but not necessarily indicative of a larger hawkish worldview that deserves challenging. To be sure, Sanders did note that the policy of regime change that Clinton has supported many times has lead to disaster, but it was a point glancingly made, backed up by historical allusions to events in the 1950s. He failed to produce specific attacks about positions Clinton advocated as secretary of state concerning Syria and Libya. He framed his attack on Clinton in a way that lessened the impact.