The favorite theme of the cable news networks is that the candidacy of Hillary Clinton is in trouble. I think they promote that idea because they just want people to tune in, and they think a close race will increase their viewership. The polls tell us something different -- that Hillary Clinton is still the choice of a majority of Democratic voters.
The YouGov Poll was done between February 24th and 27th of a random national sample of 642 Democrats. No margin of error was given for just Democrats.
The CNN / ORC Poll was done between February 24th and 27th of a random national sample of 418 Democrats, and has a margin of error of 5 points.
The Rasmussen Poll was done between February 25th and 28th of a random national sample of 541 likely Democratic voters, and has a margin of error of 4.5 points.
As you can see, these newest national polls show Clinton has a lead of between 22 and 39 points.