What is bail in the US criminal justice system and what is its purpose

Answer the following questions in complete sentences.  Include in text citations and sources. 

1.  What is bail in the US criminal justice system and what is its purpose?
2. What are the choices a judge/magistrate has when determining a defendant's pre-trial status? 
3. Why was there a call for bail reform and what changes were enacted in states that reformed their bail systems?
4. Identify one issue that you think is a problem in the current bail system in the US and propose a program/law/policy  that you think would address that isssue and explain why.