- Wisconsin Gov. Scott Walker is the 15th declared Republican presidential candidate this cycle
- He made his announcement in a tweet Monday morning and he's holding an event this evening
- Walker's claim to conservative fame came from surviving a recall effort following an extended labor fight in his state
- Walker has been polling ahead in the important early caucus state of Iowa
(CNN)Scott Walker, the political phenomenon who rose to national fame by taking on unions in one of the most blue-collar states, announced Monday that he'll seek the Republican nomination for president, using his kick-off rally to throw red meat to his conservative supporters.