Wisconsin Gov. Scott Walker on Monday evening announced his bid for the Republican presidential nomination, vowing to be a Washington reformer and telling potential voters that as president he would “fight and win for America.”

The two-term governor enters a crowded 2016 field with hopes he can recapture some of his early momentum.

“After a great deal of thought and a whole lot of prayer, we are so honored to have you join with us today as we officially announce that we are running to serve as your president of the United States of America,” Walker, joined by his wife and two sons, told the crowd in Waukesha, Wis.

The 47-year-old Walker wasted little time in his roughly 45-minute speech getting to his successful 2011 battle with labor unions, which included a 2012 recall-election victory and which has become his political calling card.

“My record shows that I know how to fight,” he said. “And I know now, more than ever, that Americans need a president who can fight and win for America.”

More On This...

Although he lacks the foreign-policy experience of others in the GOP field of 15, Walker devoted much of his speech to vowing to fix the global crises that now concern the United States -- from Russian aggression and cyber-hacking to improving strained relations with Israel and the threat of the Islamic State and other terror groups.

The latest headlines on the 2016 elections from the biggest name in politics. See Latest Coverage →

“The U.S. needs a foreign policy that will put steel in front of our enemies,” said Walker, who vowed to keep Americans and future generations safe from ISIS.

“The commander in chief has a sacred duty to protect the people,” he said.

Speaking to Fox News' Sean Hannity hours before the U.S. and five other world powers concluded a formal nuclear deal with Iran, Walker vowed to "terminate" any such agreement "on my very first day."

"I would then put in place crippling economic sanctions against Iran," Walker said, "and I’d convince our allies that this is not a country we should be doing business with."

Walker also vowed to grow the U.S. economy as well as cut taxes and improve education by eliminating seniority and tenure, just as he did in Wisconsin.

"I think you have to take big chunks of the federal government out of Washington and send it back to the states," Walker told Hannity. "Medicaid, transportation, workforce development, even education ... Think about it. The states are more effective, more efficient, and definitely more accountable to the American people."

Earlier in the day, Walker announced his bid in an email to supporters, saying in part, "It’s time to take the successes we have created in Wisconsin and apply them to Washington."

Walker, first elected governor in 2010, enacted policies weakening the unions' political power and became the first governor in U.S. history to defeat a recall election.

He also cut income and corporate taxes by nearly $2 billion, lowered property taxes, legalized the carrying of concealed weapons, made abortions more difficult to obtain, required photo identification when voting and made Wisconsin a right-to-work state.

His budget this year, which plugged a $2.2 billion shortfall when he signed it into law Sunday, requires drug screenings for public benefit recipients, expands the private school voucher program, freezes tuition at the University of Wisconsin while cutting funding by $250 million and removing tenure protections from state law.

Such achievements may appeal to conservatives who hold outsized sway in Republican primaries, yet some could create challenges in a general election should Walker ultimately become the GOP's nominee. Voter ID laws, abortion restrictions, liberal gun policies and education cuts are not necessarily popular among swing-state independents.

Despite his late entry, Walker has been near the top of polls since the start of the election cycle.

He has nearly 11 percent of the vote, trailing front-running Jeb Bush, the former Florida governor, who has roughly 16 percent, in the most recent averaging of polls by the nonpartisan website RealClearPolitics.com.

He now travels to Nevada and Georgia and early primary states South Carolina, New Hampshire and Iowa. He begins the first leg of his official campaign on Tuesday in Nevada with a stop at a Harley-Davidson shop in Las Vegas.

Walker has traveled overseas four times this year. His visit to Israel in May was tightly controlled, with no public appearances. He stumbled rhetorically at times during a more public London tour earlier. He faced sharp criticism for a speech in February in which he said his experience taking on thousands of protesters in his state during his battle with unions has prepared him to confront terrorists abroad.

He supports Wisconsin's first-in-the-nation school voucher program. Walker extended the program statewide after its start in Milwaukee and Racine and this year proposed eliminating enrollment caps.

Walker's position has varied on Common Core academic standards. He never explicitly advocated for them, but in his first state budget in 2011 he called for statewide tests that were tied to the standards. His budget this year prohibits the state superintendent from forcing local school districts to adopt the standards and calls for new standardized tests.

Democrats have for months been sharpening their political attack on Walker and his announcement.

On Saturday, the Democratic National Committee released an email titled "Six facts you need to know about Scott Walker" that included criticism about his record of job-growth in Wisconsin and his comments about how his union-related battles have made him ready to confront international terrorists.

Democratic National Committee Chair Rep. Debbie Wasserman Schultz said in a statement that Walker “promised to eliminate the deficit but his state has $2.2 billion in the red, and Walker’s Wisconsin sits at the bottom in his region for job growth.”

“It’s that type of divisive, ineffective politics, and mismanagement that middle class Americans don’t need any more of in Washington,” she said. “Walker simply has the wrong priorities for America."

If elected, Walker would be the first president since Harry Truman, elected nearly 70 years ago, without a college degree.

He attended Marquette University in Milwaukee but dropped out 34 credits short of graduation to take a Red Cross job.

The Associated Press contributed to this report.