Truly ambivalent:
Immigration
Affirmative action
Prostitution
National debt (i.e. how much to prioritize paying it down)
Single-payer healthcare (vs. a less ambitious plan)
$15 minimum wage (vs. $12 min. wage)
Can see both sides (but generally take the left-wing position):
Guns
Abortion
Military spending
Drug decriminalization
Free trade (which I don't consider a left vs. right issue)
What aren't you ambivalent about then?
To name a few: more of a federal role in healthcare (e.g. I'd love to just make everyone eligible for the current version of Medicare), carbon tax, investments in renewable energy, higher taxes on high earners, vastly increased federal aid for education, a federal law mandating independent redistricting commissions, stricter anti-trust laws, capital punishment (anti), the CFPB (pro), greater funding for mass transit, right to work laws (anti), NATO (pro), Cuban thaw (pro), gay marriage (pro)
