The constitution does not give the government the power to appropriate funds for infrastructure. But hey, that never stopped power hungry megalonmaniacs from wasting tax payer dollars.
If Bernie Sanders wants to make such a vast proposal he should do it the legal way and propose a constitutional amendment. Of course, he knows that will never happen so he'll just unconstitutionally let congress force it through if he wants.
Of course, it's all talk now because he's not the president.
If people want government high speed internet so bad they should be lobbying their STATE government because that is where the power in the constitution lies.