People take Coulter seriously in 2015? Come on. She also thinks Trump can win the presidency.
If you think a socialist can win the presidency in the US in 2016 you're delusional. He'd be outspent and crushed by bullshit ads 24/7.
Sanders in polling wins against the entire republican field just like Hilary does. He beats some candidates such as Trump even more soundly than Clinton. The latest polling has Hilary at only +5 on Trump with Sanders is beating him at +10.
In presidential politics, money has much more of an impact during the primary. Once the candidate is nominated, there is so much free press and attention thrown towards both the candidates that you can't really "crush" a candidate with ads the way you can in a congressional seat in an off year for example.
Sanders openly being a socialist is really only an issue if he backpedals away from it the way most democrats run away from the allegation. Someone calls Sanders at a debate and Sanders will respond with "Yes. I believe that Medicare and Medicaid are great socialist institutions and I will preserve them and expand them to all citizens" and it's not going to impact him.
Sander's biggest obstacle towards the Presidency is Hilary.