What is the multiplier effect of investing political capital in increasing union density?

I wonder what is the multiplier effect of investing political capital in increasing union density?
 
http://www.nytimes.com/2016/02/16/us/politics/left-leaning-economists-question-cost-of-bernie-sanderss-plans.html?smid=tw-share&_r=1

” They worry that Mr. Sanders, as president, would exhaust his political capital on what they call a fool’s errand, at the expense of other initiatives on education, infrastructure, climate change, worker benefits — and the Affordable Care Act itself. "

” if Mr. Sanders were elected and fought for a single-payer plan, it ‘would rapidly destroy his administration by using up every ounce of political capital he’s got.’ ”

My comment over at Economists View:
The answer is to build up an unbeatable mountain of political capita by rebuilding union density. How? Starting in progressive states with Democratic legislative majorities — make union busting a felony.

There are all sorts of restrictions on union bargaining methods — e.g., no secondary picket lines — that are enforceable. None of the restrictions on illegal union busting are the slightest bit enforceable.

Make unions attractive by example — let people in red states see how positively they work — make people in red states jealous. Change the culture — get more union states. Then — on only then — we can get everything we want.