By Rachel E. Stassen-Berger and Glenn Howatt

Outside groups -- unions, Democratic and Republican supporters and PACs set up just to support a single candidate -- have raised at least $15 million since the 2012 election.

Those outside groups, which had been slowly raising cash in preparation for the 2014 elections, began piling on money in earnest this summer. Since June 1, the largest independent spending groups raised more than $2.6 million, according to reports released Tuesday.

 As with previous election cycles, union organizations are gearing up with big cash. Education Minnesota, the state’s teachers union, led in fundraising among outside groups with $1.8 million already raised. All told, union affiliated PACs have raised more than $4.6 million to train on the 2014 election.

Much of that cash will benefit Democratic candidates and the Democratic Alliance for a Better Minnesota, which, with its supporters, has already brought in more than $1.8 million.

Republicans-leaning outside groups have already raised $2.6 million. The largest among them, the Freedom Club, launched a major television ad campaign against Dayton in July.

See a breakdown of the fundraising by some of the major outside groups below: