well, it's probably an underestimate, actually - "fuck the two party system" is actually running close to thirty percent right now - and arguably ahead of trump.
i've pointed out previously that i don't think the libertarians can hold that - presuming trump aligns with his party. on the other hand, the more that clinton aligns with her party, the more she alienates green supporters. that's a very different dynamic: trump gets stronger as he moderates for the general, whereas clinton gets weaker.
if jill stein can hold those numbers, they could very well double overnight once the word gets out. if that happens, she's going to hit a bit of a brick wall around 15%, in the short run. but, if she can get there, that support may be permanent.
like i say: tipping points. half of 50 is 25. that's too much. 15-20 isn't. then, we've got a three-way race and the debates over what people actually want can begin.
http://i2.cdn.turner.com/cnn/2016/images/06/21/rel7b.-.2016.general.pdf
^lots of ifs, there, of course. hypotheticals on hypotheticals.
just, don't be shocked. it's plausible.