Scott Walker: 'I'm in. I'm running for president'

With a tweet, Wisconsin Gov. Scott Walker announced his candidacy for the presidency Monday morning.

"I'm in. I'm running for president because Americans deserve a leader who will fight and win for them - SW ScottWalker.com #Walker 16," he wrote.

He said in an accompanying video: "America needs new, fresh leadership with big, bold ideas from outside of Washington to actually get things done. in Wisconsin, we didn't nibble around the edges. We enacted big, bold reforms that took power out of the hands of the big government special interests and gave it to the hard-working taxpayers, and people's lives are better because of it. We fought and won. In the Republican field, there are some who are good fighters, but they haven't won those battles."

Later, a crowd of about 3,000 was due to gather at the Waukesha County Expo Center in Wisconsin for a personal message from Walker, and a formal verbal announcement for his campaign.

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"It's historic for the state when you have a governor announcing he's running for president," said Waukesha Mayor Shawn Reilly, Fox 6 Now reported. "To have it done in Waukesha also makes it historic for the city ... The name Waukesha will pretty much be on every single news channel."

Walker is the 15th Republican candidate to seek the party nod for the presidency.

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The New York Times reported Walker is positioning himself as the "authentic" and level-headed candidate in a crowded field that includes evangelicals, moderates and those who have tried on prior occasions to win the Republican nomination for the White House.

"[He has] a lot going for him," said Iowa Gov. Terry Branstad, the New York Times reported, "given that he's a neighboring state governor who has been tried and tested on tough issues."