Zogby: Why polls are often skewed

The 2020 race for the White House is well underway, and so are the polls.

Several recent polls have shown US President Donald Trump trailing those leading the pack of Democrats seeking their party's nomination. But Trump has always dismissed those polls, or at least those he doesn't like, as more examples of "fake news".

Is it possible to accurately handicap the current stampede of Democratic candidates and make a reasonable estimate about who might win, or at least who's ahead?