All this, of course, raises the question of why Warren’s ascent has been arrested. Given the timing, it’s fair to wonder whether the fourth debate had anything to do with it; after all, Warren did come under increased fire from Buttigieg, Biden and others, perhaps due to her perceived status as a front-runner in the race. At the very least, it certainly didn’t seem to help her as much as the third debate, which was followed by particularly big spikes for Warren in the RealClearPolitics average, my experimental average and several individual polls.

More broadly, criticism of Warren’s lack of a concrete health care plan may have finally gotten through to voters. Both at the debate and on the campaign trail, she evaded questions about how she would pay for her “Medicare for All” plan until her campaign, tacitly acknowledging the pressure, released a more detailed plan last week. On the other hand, maybe it has nothing to do with Warren at all and just reflects other candidates holding their own or picking up ground. For example, some of the polls and polling averages show Sen. Bernie Sanders and South Bend, Indiana, Mayor Pete Buttigieg ticking up a point or two in recent weeks; that support had to come from somewhere.