Well, why aren't they? They weren't challenged at the debates. They aren't challenged by the press. The GOP doesn't bring them up. I don't get it.
1. Because the Dems don't want to encourage their own Populist Rebels any more than is necessary before the Anointing at the Convention
2. Because the Dems want to maintain the illusion of a united facade for as long as they can to the greatest extent they can
3. Because the Pubs want Bernie to win - knocking out Hillary, whom they consider more difficult to beat
4. Because - if Bernie wins the nomination - the Pubs will wait until
AFTER the Anointing at the Convention, and
THEN pounce on his policies like flies on shit
Illusion and Timing are all, from one vantage point or another...