The problem with 2020 presidential polls

A Quinnipiac poll released Thursday has Elizabeth Warren leading by seven points in the 2020 Democratic race while a Wednesday CNN poll gave Joe Biden a 15-point advantage — both among their biggest polling leads so far.

Why it matters: Those back-to-back — and seemingly contradictory — results highlight why looking at a single poll in isolation cannot paint an accurate picture of what's happening in the race, especially months before the first votes are officially cast.