Joe Biden and Elizabeth Warren are the top two candidates in the presidential race, according to most polls taken since last week’s debate. Of the five national polls taken since then, all show the former vice president continuing to lead, and four show Warren in second place — and Vermont Sen. Bernie Sanders in third. (The fifth poll shows Sanders in second and Warren in third). A poll from NBC News and the Wall Street Journal shows Warren 11 points ahead of Sanders, but polls from HarrisX, SurveyUSA, and YouGov show her leading him by 1 to 4 points, and a Morning Consult poll shows her trailing Sanders by 2. On average, that’s a 3.2 percent margin for Warren over Sanders. That’s bigger than before, but it’s not clear whether it will hold up (or expand) in the coming weeks. As for the other candidates, the worst news is for California Sen. Kamala Harris. Every new national poll shows her clearly falling behind the top three candidates. In fact, she’s barely ahead of South Bend Mayor Pete Buttigieg in two polls, tied with him in a third, and trails him in the other two. And beyond the top five, Andrew Yang, Beto O’Rourke, and Cory Booker all have about 3 percent support each in...