Talk politics.

The difference is whether something has no basis whatsoever in fact, or whether you just have to stretch really, really hard to make the claim you're making. The two biggest ones I can think of are Romney's red-meat attacks: that Obama cut $700+ billion from Medicare, and that he "gutted" the work requirement. Both are sorta true, if you squint really hard and turn your head like a dog waiting on a treat. In reality, Obama cut Medicare payouts, not benefits, by adjusting reimbursement rates, and the work requirement went away in select states that wanted to experiment with a different mechanism, and in return promised higher results. The base-line is correct ("Medicare spending will drop $700b" and "some states no longer have a work requirement for welfare") but the actual circumstances are vastly different.

That's the difference between bullshit and lies: one has a kernel of truth, intermingled like a piece of undigested corn, and the other is just a sloppy light-brown mess. Of course, the guy serving up the former will point to that one piece of corn, tell you "It's got food in it!" and act offended when you turn it down.