AFL-CIO President Richard Trumka kept it brief in his response to the announcement that Wisconsin Gov. Scott Walker was officially running for the Republican presidential nomination.

Trumka issued a six-word press release: "Scott Walker is a national disgrace."

That was it. Trumka added nothing to clarify or expand on the thought. He said in a tweet that was his "full statement."

With the possible exception of GOP presidential candidate Mike Huckabee, there is little love lost between organized labor and the Republican Party these days. But union leaders such as Trumka hold a special contempt for Walker, who famously weathered massive protests by Badger State unions and their liberal allies in 2011 to push through major reforms of the state's public-sector union system.

The changes limited collective bargaining to just wages as well as allowing public-sector workers to opt out of paying union dues. The reform also ended automatic union dues deduction by the state and required unions to engage in annual recertification votes, meaning they lose recognition if a majority of members do not affirm they want to remain in the union.

The reforms have had a devastating impact on the state's public-sector unions, with thousands of workers who previously had no choice now taking advantage of their new right to simply leave. The local branches of the American Federation of State, County and Municipal Employees have lost between a third to a half of their members, losing much of the financial and political clout in the process.

It was organized labor that was largely behind the recall election Walker faced in 2012. Unions campaigned heavily against him in the 2014 election as well. Both were bitter defeats.

"Scott Walker has sinisterly shown us the reality of how money pollutes politics. Everybody knows Scott Walker does not share Wisconsin's values and cares more about his own political ambition," a somewhat more talkative Trumka said after Walker's win last year.

In March, Walker signed a bill making Wisconsin a "right-to-work" state, meaning that all workers, public and private sector, would no longer be required to join or otherwise support a union as a requirement of employment. This means that unions in the state soon may face membership losses. Labor leaders fumed, noting that Walker had previously said that he didn't think the state needed such a law, but changed his mind when the legislature passed one.