Republican jockeying before the 2016 presidential primary season is becoming a contest over who will become the alternative to the Tea Party's candidate.

Kentucky Sen. Rand Paul is the favorite of the small-government movement, and Republican rivals are starting to gang up on him to argue that he could dim the party's chances against a Democratic Party unified behind Hillary Rodham Clinton.

Texas Gov. Rick Perry delivered a rebuke of Paul in the Washington Post, casting him as an isolationist who would let terrorism fester beyond U.S. borders.

Paul is "curiously blind" to the threat of the Islamic State in Iraq and "drawing his own red line along the water's edge, creating a giant moat where superpowers can retire from the world," Perry wrote in a July 11 opinion piece.

"I'm with Perry on that," former Pennsylvania Sen. Rick Santorum, a failed candidate in 2012 Republican primary, said Sunday on NBC's "Meet the Press."

Ohio Sen. Rob Portman told Bloomberg News last week he may run for president if he doesn't see a viable Republican candidate with the experience and temperament to manipulate the levers of power in Washington — an implicit criticism of Paul.

Paul has argued for a less interventionist foreign policy by the United States than many Republicans support, pushing for more scrutiny in distinguishing between the country's vital and peripheral interests. He has also angered some Republicans by saying he doesn't blame President Obama for the current turmoil in Iraq, pointing the finger partly at those who originally supported the war.

Paul works to expand base

As much as other Republicans are maneuvering to develop the anti-Paul brand, he is working to expand his party base, an effort punctuated by his trip this weekend to Sun Valley, Idaho, to participate in the annual Allen & Co. conference, a gathering of top business executives.

For most Republican presidential aspirants, the primary challenge is finding the space between Democrat Clinton and Tea Party-aligned Paul.

Paul fashioned a reputation as a populist crusader in 2010, winning his Senate seat with tough talk about Wall Street and American overextension abroad against the backdrop of the 2008 financial crisis and the U.S. invasion Of Iraq.

Last year, he spoke for almost 13 hours on the Senate floor against American drone policy, an effort that ranked among the longest filibusters in history.

Paul has distinguished himself from other Tea Party favorites, such as Republican Sen. Ted Cruz of Texas, and even from his own father, former Texas Rep. and presidential candidate Ron Paul, by working to expand his network beyond the movement.

He has befriended Nate Morris, the chief executive of Lexington, Ky.-based waste-management company Rubicon Global, who was former President George W. Bush's youngest campaign bundler in 2004.

While he admonished Republicans in April that they can't be the party of "fat cats, rich people and Wall Street," Paul's biggest supporters include employees of Mason Capital Management, a $13.6 billion New York hedge fund, where 17 of 33 investors have given to his political apparatus.

At the Idaho conference, Paul met with Facebook founder Mark Zuckerberg and Clarium Capital Management President Peter Thiel, an early Facebook investor, according to Politico.