Some Questions about Labor/Environment Provisions in Trade Agreements

This Presidential campaign has made it very clear that there are a number of people (mostly Democrats, I would guess), including the two remaining Democratic Presidential candidates, whose support for trade agreements is conditional on having enforceable labor and environmental rules as part of these agreements.  This view raises a number of questions for me.  These are rhetorical, but people are free to offer their thoughts, of course.

1.  Would those who support putting enforceable labor/environment rules in trade agreements prefer to have these rules in free-standing mutilateral agreements on these issues, outside the context of trade agreements?  If so, why not try to make the case for that?  In other words, why aren't Obama, Clinton and others arguing for, say, an independent, binding, enforeable international agreement on labor protections?   If that approach is rejected, then go the trade agreement route, but why not start there?

2. How realistic is it to think that certain U.S. trading partners will agree to having labor and environmental rules in trade agreements?  By demanding inclusion of labor/environment rules, aren't we just ensuring that many of these agreements do not get signed?

3. The unstated assumption seems to be that the U.S. can use these provisions to ensure that our trading partners follow the rules.  But do those who support these provisions anticipate complaints being brought against the U.S. under binding labor/environment rules?  If yes, would that be a good thing?

4. By how much, if at all, do supporters of this view believe that inclusion of these rules in the NAFTA and other trade agreements will reduce the number of U.S. job losses caused by trade agreements?

5. What is the scope of the labor/environment rules that should be included?  For example, would a minimum wage be included in the labor protections?