What's really behind the attempted destruction of the great teachers' unions?

Substantial as the stakes may be for Big Labor, they are even higher for Mr. Obama and his party. This is all because of a January 2010 decision of the U.S. Supreme Court called Citizens United v. Federal Election Commission,130 S.Ct. 876 (2010) in which a majority of the Supremes held:
(1) the government may not, under the First Amendment, suppress political speech on the basis of the speaker's corporate identity, overruling Austin v. Michigan Chamber of Commerce, 494 U.S. 652, 110 S.Ct. 1391, 108 L.Ed.2d 652; and,
(2) the federal statute barring independent corporate expenditures for electioneering communications violated First Amendment, overruling McConnell v. Federal Election Com'n, 540 U.S. 93, 124 S.Ct. 619, 157 L.Ed.2d 491.
While the GOP enjoys the support of numerous corporations, which were freed from restraints on the levels of financial support they can funnel to Republican candidates, the Democrats have far fewer such super-supporters. Big Labor is, as always, the biggest of the big donors on the Democratic side of the political divide. Thus, destruction of the powerful public-sector unions, which are the backbone of Big Labor, would be a blow not only to their millions of members, but to the Democratic Party, as well.