LOUISVILLE, Ky. (AP) — Sen. Rand Paul launched his 2016 presidential campaign Tuesday with a combative message against both Washington and his fellow Republicans, declaring that "we have come to take our country back."

The fiery message, delivered in his home state of Kentucky before he jetted to four early-nominating states, was set to motivate legions of supporters from his father's two earlier unsuccessful bids for the Republicans' presidential nomination, as well as broaden his appeal outside of the typical GOP coalition.

"I worry that the opportunity and hope are slipping away for our sons and daughters," Paul said in a speech that tried to tap into Americans' deep frustration with Washington. "What kind of America will our grandchildren see?"

He added: "It seems to me that both parties and the entire political system are to blame."

By criticizing his own party, the tea party favorite was trying to distinguish himself as different than the typical politicians he was deriding.

Cheers erupted when he decried government searches of phones and computer records as a threat to civil liberties. Most Republicans defend the practice as a necessary defense against terrorism, but Paul said the programs only provide a false sense of security.

"I say that your phone records are yours. I say the phone records of law-abiding citizens are none of their damn business," Paul said.

At a splashy kickoff rally with videos, a series of guest speakers and a cameo from his father, Paul promised a government restrained by the Constitution and beholden no more to special interests.

"I have a message, a message that is loud and clear and does not mince words," he told cheering supporters. "We have come to take our country back."

Paul is a fierce critic of Washington, where he is in his first term as a senator but seldom in line with his party's leadership. A banner over the stage in Louisville proclaimed: "Defeat the Washington machine. Unleash the American dream."

Paul's challenge now is to convince Republican primary voters and caucus-goers that his is a vision worthy of the GOP presidential nomination, a prize twice denied his father, former Rep. Ron Paul of Texas, who joined him at Tuesday's announcement and earned a raucous cheer when he was introduced.

Many in the ballroom said they had been backers of Ron Paul's presidential runs.

"Rand, I think, encompasses those same principles, but he also realizes the pragmatism that is necessary to bring those principles to fruition in American politics today," Eric Thomas, a 49-year-old financial services worker from Knoxville, Tennessee, said at Paul's event.

Paul begins the 2016 race as just the second fully declared candidate, behind Sen. Ted Cruz of Texas, but he could face as many as 20 rivals for the nomination before the lead-off Iowa caucuses in February.

Along the way, Paul is likely to challenge his fellow Republicans' views on both foreign and domestic policy, as well as the nuts and bolts of how campaigns are run. Tech savvy and youth-focused, Paul is expected to be an Internet pacesetter that his competitors will be forced to chase.

After his speech in Louisville, Paul planned to answer questions from voters on his Facebook page and visit the first four nominating states: New Hampshire, South Carolina, Iowa and Nevada. Before his announcement, he was already selling on his website iPhone cases branded with his logo, signed copies of the Constitution and Rand Paul beer steins.

The online store was a quick way for Paul to collect contact information for voters who want the swag but had not yet considered a direct donation to the candidate. It's unclear, though, how much support he can muster in the Republican mainstream.

Paul is a frequent contrarian against his party's orthodoxy, questioning the size of the U.S. military and proposing relaxation of some drug laws that imprison offenders at a high cost to taxpayers. He also challenges the GOP's support for surveillance programs, drone policies and sanctions on Iran and Cuba.

But as the presidential campaign has come closer, Paul has shifted his approach somewhat on the complicated question about how much government the country actually needs.

In Paul's proposal for the 2012 budget, he called for reducing military spending and for fewer troops at the Department of Defense. But last month Paul proposed a 16 percent increase in the Pentagon's budget.

In another sign of his uphill climb, an outside group not connected to any candidate planned to spend more than $1 million on ads criticizing Paul's positions on Iran sanctions. And Democratic National Committee chairwoman Debbie Wasserman Schultz continued the pile-on, telling reporters, "Rand Paul's policies are way outside the mainstream."

Perhaps reflecting the challenges he faces in convincing his critics he deserves the nomination, Paul is also leaving open the door to a second term in the Senate. With the backing of his state's senior senator, Majority Leader Mitch McConnell, Paul is likely to seek the White House and the Senate seat at the same time.

One of Paul's likely rivals, Sen. Marco Rubio of Florida, has said he would not double-dip on the ballot. He is expected to announce next week that he will skip a Senate re-election bid in 2016 in favor of putting everything into a presidential campaign.

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Elliott reported from Washington.

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(Photo: AP Photo/Carolyn Kaster)