Watch "The Situation Room with Wolf Blitzer" Wednesday at 5 p.m. ET for an interview with Rand Paul.
Louisville, Kentucky (CNN)For Rand Paul, it's all led to this moment.
Since riding the tea party wave into the Senate in 2010, Paul has carefully built a brand of mainstream libertarianism -- dogged advocacy of civil liberties combined with an anti-interventionist foreign policy and general support for family values -- that he bets will create a coalition of younger voters and traditional Republicans to usher him into the White House.
The test of that theory began Tuesday when the Kentucky senator made official what has been clear for years: He's running for president.
"Today I announce with God's help, with the help of liberty lovers everywhere, that I'm putting myself forward as a candidate for president of the United States of America," Paul said at a rally in Louisville.
Paul immediately hit the campaign trail for a four-day swing through New Hampshire, South Carolina, Iowa and Nevada -- the states that traditionally vote first in the primaries and caucuses.
In his speech, he called for reforming Washington by pushing for term limits and a constitutional amendment to balance the budget. He argued that both parties are to blame for the rising debt, saying it doubled under a Republican administration and tripled under Obama.
"Government should be restrained and freedom should be maximized," he said.
The line-up of speakers who introduced Paul sought to paint the senator as a nontraditional candidate with diverse appeal, and by the time he got on stage, he was the first white man to address the crowd.
The speakers included J.C. Watts, a former congressman who's African-American; state Sen. Ralph Alvarado, who's Hispanic; local pastor Jerry Stephenson, who's African American and a former Democrat; and University of Kentucky student Lauren Bosler.
"He goes everywhere. It doesn't matter what color you are. Rand Paul will be there," Stephenson said, firing up the crowd.
So far, Paul joins only Texas Sen. Ted Cruz as a declared candidate for the GOP presidential nomination. "His entry into the race will no doubt raise the bar of competition," Cruz said in a statement welcoming Paul into the race.
But the field is certain to grow in the months ahead with Jeb Bush, Chris Christie, Scott Walker, Lindsey Graham and others eyeing a campaign. Marco Rubio, a Florida GOP senator, is expected to launch his campaign next week.
Bush, who said his 2016 decision is a "while off," told reporters in Colorado Springs on Tuesday that "libertarianism definitely has a place in the GOP" but stressed that he differs with Paul on foreign policy.
For now, the nomination is up for grabs with no clear front-runner. Paul came in third place at 12% in a CNN/ORC International Poll of Republicans. Bush led the pack at 16% while Walker came in second at 13%.
Ron vs. Rand Paul
Paul, the son of former Texas congressman and three-time presidential hopeful Ron Paul, will build on his father's legacy as a candidate eager to bring civil liberties to the forefront of the national dialogue. He's already used his perch on Capitol Hill to draw attention to those issues, including a 13-hour filibuster two years ago blasting the Obama administration's drone policies and a lawsuit against the National Security Agency's phone metadata collection effort.
But Paul, 52, will split from his father in one important way: his approach to the campaign. Where Ron Paul often focused on creating a libertarian movement, Rand Paul is planning a more strategic, less purist operation that could have a hope of competing in a general election.
The elder Paul sat on stage at the rally on Tuesday with his wife, though he's not expected to be a public face for his son's campaign. He merely attended the event as a "proud papa," a source close to the senator said.
Elected in 2010 with strong tea-party support, Rand Paul quickly rose to national fame in part due to his father's back-to-back White House runs in 2008 and 2012, but also because of Rand Paul's willingness to fight fellow Republicans.
He engaged in a war of words with Chris Christie two years ago over national security and federal spending and, more recently, he's taken swipes at Bush over issues like Common Core and medical marijuana.
Still, Paul has carefully worked to form inroads with establishment Republicans and other factions of the party's base. He's done so by becoming close political allies with Senate Majority Leader Mitch McConnell and backing mainstream candidates who competed against libertarian opponents during last year's midterms.
He's also tried to make peace with national security Republicans, taking nuanced positions that try to shed an isolationist label while still showing his apprehension toward foreign intervention. Last year, for example, he supported limited airstrikes against ISIS but vigorously fought against arming Syrian rebels.
While he bills himself as a conservative realist, Paul still tries to wear the mantle as the Republican most reluctant to take the country into war.
War's 'unintended consequence'
"I can tell you there will be one loud voice in our party saying, think of the unintended consequence," Paul said in Iowa two months ago. "Think about what we're going to accomplish and whether it will work before we go to war.' I promise you that will always be something I take very, very seriously."
The cautious foreign policy dance has drawn criticism from his father's supporters, who say Paul has become too moderate, and from hawkish Republicans who fear he wouldn't go far enough as commander in chief to tackle problems overseas. Democrats and some Republicans, meanwhile, have accused him of flip-flopping and pandering to donors.
On Tuesday, the Foundation for a Secure & Prosperous America -- a hawkish group from the right -- released a $1 million television ad buy against Paul's foreign policy, which hits the airwaves nationally on cable, as well as in the key early states that Paul will visit this week.
"Rand Paul is wrong and dangerous," says the narrator in the 30-second spot, arguing that Paul doesn't understand the threat of Iran's nuclear program. The ad ends with an image of a nuclear bomb detonating.
Paul had been silent on the Iran deal until his speech on Tuesday, when he vowed to oppose any deal that doesn't guarantee Iran gives up its nuclear ambition.
He also sought to sound aggressive on terrorism. "The enemy is radical Islam and not only will I name the enemy, I will do what ever it takes to defend America from these haters of mankind," he said.
In an interview later Tuesday, Paul argued that the ad was "crazy" and represented what he called the "the naivety of the neocons."
"These loud, sort of juvenile voices putting pictures of bombs on ads, these are the people who are so reckless that it would be a grave danger to our country to ever have these people in charge of our country," he said in an interview with Sean Hannity on Fox News.
In the same interview, Paul also weighed in for the first time on the religious freedom debate that took center stage last week after an Indiana law -- which has since been changed-- came under fire for what critics said was discrimination against gay and lesbian couples getting married.
The 2016 Republican field largely came out in defense of the law, standing by the rights of small business owners such as florists and bakers to decline participating in same-sex weddings. Paul said he felt the law was "unnecessary" and that the country's founding fathers would be "aghast" that laws needed to be in place to protect religious rights.
"That being said," he added. "I think the law ought to be neutral and we shouldn't treat people unfairly."
Asked which takes precedence, religious liberty or same-sex marriage rights, Paul said, "freedom."
"I don't think you can have coercion in a free society very well," he said. "So I would think we ought to try freedom in most of these things."
Paul is actually running for two offices at the same time, trying to hold onto his Senate seat while also running for president. Kentucky's election laws say candidates can't appear on a ballot twice, but with reluctant support from McConnell, a Kentucky powerhouse, the state's GOP will likely change its presidential preference vote from a primary to a caucus. That would allow Paul to get around the rule.
His interest in the Oval Office has never really been a secret. Shortly after the 2012 presidential election, he started crisscrossing the country to paint himself as a nontraditional Republican eager to court voters who don't typically live and vote in red areas.
He spoke at historically black colleges and universities, as well as Democratic strongholds like inner city Detroit and the University of California, Berkeley, focusing on criminal justice reform and civil liberties, two issues he believes can bring more people into the Republican Party.
"Liberal policies have failed our inner cities," he said Tuesday. "Our schools are not equal and the poverty gap continues to widen."
But Democrats are eager to paint Paul as another member of the "same old Republican Party."
"On issue after issue his policies are the same as the rest of the GOP, but even more extreme, and will turn back the clock on the progress we have made," said Democratic National Committee chairwoman Debbie Wasserman Schultz in a statement.
As one of the few national politicians who went to Ferguson, Missouri, Paul frequently boasts that there is no "bigger defender of minority rights in the Congress" than himself.
But those efforts could prove futile if he can't get beyond controversial comments he made in 2010, when he questioned parts of the Civil Rights Act, especially provisions that place restrictions on private property.
He's steered clear of such hot-button issues more recently. Last week, for example, he was one of the few Republicans who didn't weigh in on religious freedom laws in Indiana and Arkansas that critics argued would allow businesses to discriminate against gays and lesbians.
Paul has also worked to maintain a following that includes a large swath of young voters who he partly inherited from his father. Heavy on tech and social media, his political team has opened an office in Austin, Texas, and will soon establish one in the heart of Silicon Valley. Like clockwork, Paul frequently holds up his phone during his stump speech and declares that what people do on their smartphones is "none of the government's damn business."
His nontraditional style is complemented by Paul's wardrobe. The senator is known for wearing blue jeans with boots and a blazer when he's on the trail, and during the winter, he opts for a turtleneck and sport coat rather than a tie.
But in his quest to become a national figure, Paul's comments have come under scrutiny and some of his statements have led critics to question whether he's ready for prime time. Earlier this year, Paul, an ophthalmologist, lent credibility to theories that vaccinations cause mental disorders, and last fall he caused a stir when suggesting that people could catch Ebola at cocktail parties.
And while he's not media shy—he's given hundreds of interviews in the past year alone—Paul can get short-tempered with reporters. He shushed a female interviewer in February, and last fall he blew up at a reporter who asked a question about foreign aid to Israel.