a president has limitations. but without a president who wants to make change happen, changes won't happen.
by the way, i am not sure every issue is a straight red-blue choice. structural reforms can cut across party lines.
eg the campaign finance/ money-control-of-congress issue is more an incumbents-versus-challengers thing. it is as appealing to a person with rand paul's principles (which lead him to challenge his party's leadership) as much as to someone like bernie.
with such a tiny turnover of personnel in the senate, for instance, people should be screaming for a change.