Which Republican has the most to prove at CPAC 2015?

The 2015 Conservative Political Action Conference (CPAC) kicks off in Maryland Thursday, and a number of potential Republican presidential candidates are descending on the three-day event to woo the people whose votes they might need next year.

First held in 1973, CPAC has emerged as a marquee annual event for the American right wing: an opportunity for leading lights and rising stars to consult with one another and appraise the political figures who could stake a claim to their allegiance. The organizers bill the event as the "nation's largest gathering of conservatives."

"This really is the first chance that these folks will have to say before such a large audience, 'This is who I am, this is what I believe in,'" said Ross Hemminger, a spokesman for the American Conservative Union, which spearheads CPAC.

The conference takes on an added sense of urgency in the year before a presidential race, as battle lines are drawn and the jockeying among potential GOP primary rivals intensifies. That's especially true this year, with a wide-open race for the Republican nomination and no fewer than a dozen potential candidates scheduled to speak.

The speeches will provide an early look each candidate's strategy for courting the conservative base. And the potential payoff could be huge. The rapid rise of Wisconsin Gov. Scott Walker in the wake of his well-received speech at the Iowa Freedom Summit last month illustrates how quickly a rousing appearance at a conservative confab can alter the early primary landscape.

With that in mind, here's a look at the pressures and expectations some potential candidates face when they take the stage over the next three days.

Jeb Bush

Jeb Bush's signal last December that he's planning to run for president dramatically reorganized the GOP landscape heading into 2016, and the former Florida governor is already assembling formidable a team of operatives and fundraisers.

Bush is expected to post a strong showing among the GOP's donor class and its more moderate, business-friendly wing. But his speech at CPAC could demonstrate how Bush will court the party's base, which views him with suspicion due to his heterodox views on immigration and education.

"In some ways, Jeb Bush has the most to prove of anyone," said GOP pollster and strategist Frank Luntz, a CBS News contributor. "His record as governor is unassailable, but his more recent positions on immigration reform and education are problematic with the conservative base. He doesn't have to change their minds on those issues, but he does have to convince them that these issues should not disqualify him from consideration."

Rick Wilson, a Florida-based GOP strategist, said Bush "ought to show them the kind of conservative leader he was in Florida. He needs to reacquaint them with his record and his philosophy."

"He also has to show some passion," Luntz added. "His speeches in recent days have lacked the intensity and fire that crowds like the one at CPAC expect."

Chris Christie

New Jersey Gov. Chris Christie, once considered a top contender for the 2016 GOP nomination, has slipped out of the conversation recently. His appeal among the GOP's establishment wing has been corroded by the arrival of Jeb Bush, and he faces problems at home in New Jersey, including record low approval ratings and a still-simmering traffic scandal involving the George Washington Bridge.

And while his bombastic style helped make him a national figure, there is ample concern about how well it would wear over the course of a long presidential campaign.

"I think Christie has a high hill to climb at CPAC," said Wilson. "He may be trying for a reboot to show people the kind of spark and energy that he used to have is still something he can bring to a discussion."

Some aren't counting Christie out just yet, though. "Not only do I think he's still viable, I think he's one of the top three. There just needs to be a mute button added to the Christie repertoire," said Luntz. "Christie has only one volume: loud. And that pays off for this audience, but it's not enough. He needs to use CPAC to lay out a more comprehensive, positive agenda."

Scott Walker

As noted before, Walker's speech at the Iowa Freedom Summit last month catapulted him into the top tier of potential GOP contenders - juicing his early poll numbers and adding a healthy dose of name recognition. Since then, though, Walker has stumbled over questions about evolution, his lack of a college degree, and President Obama's Christian faith.

With his speech at CPAC, Walker will look to prove that he's not just the flavor of the month, but a viable candidate for the Republican nomination who can weather a rough news cycle or two (and punch back, if need be). He'll likely nod at his effort to curtail the power of public employee unions in his state - a push that earned him an unsuccessful recall election and plenty of goodwill among the GOP base.

"Walker has replaced Chris Christie as the number-two candidate for Republicans in 2016," said Luntz. "Conservatives know what he did on unions, now they need to know what he would do on other issues - it's much more informational. They are predisposed to like him. He has to turn that like into love."

"Scott Walker needs to show he's not just a flash in the pan," said Wilson. "He also needs to remind these guys that he...has been up against every single thing the Democratic hate machine can throw at him, and not only has he survived it, he's crushed them."

Rand Paul

Kentucky Sen. Rand Paul won the last two CPAC straw polls, and his supporters will be out in force at this year's conference. His libertarian leanings have endeared him to parts of the Republican base on economic policy and government surveillance issues, but they've also distinguished him from his party at times, particularly on foreign policy. GOP security hawks have been very critical of Paul, saying his aversion to foreign entanglements is simply dangerous.

At CPAC, look for Paul to emphasize those issues on which he and the conservative base align, while alleviating any doubts on issues on which they disagree.

"Rand Paul is one of the best GOP spokespeople right now," said Luntz. "When he speaks, people listen, and for the most part people like what they hear. The challenge is a single issue: foreign policy. And foreign policy does matter to the conservative faithful. Paul's position on foreign policy is not the mainstream of conservative Republicans right now. So it's an interesting challenge for him: Does he try to change them, or does he accept that the issue will always be an Achilles heel for him?"

"Rand Paul needs to show, in an era in which ISIS is rising and the loss of America's foreign status is starting to hurt us so much, that he's not just going to offer isolationism," said Wilson. "He's done some good work on that in the last two years, but not perhaps enough for people to swallow their objections."

Ted Cruz

The Republican base loves Texas Sen. Ted Cruz. The party's old bulls, though, are wary of the freshman senator, who's repeatedly clashed with GOP congressional leaders on policy and legislative strategy over the last several years. Cruz will likely bask in the adulation of a friendly crowd at CPAC, but he may also use his speech to extend an olive branch to the party establishment.

"This will be a party atmosphere for Cruz - it will be like a coronation," said Luntz. "He's got these people in his corner already, and he'll celebrate with them. But these people alone do not win the Republican primary. He needs to be able to reach people who don't attend CPAC and aren't as conservative as those in the room."

"It's good to have fluency with the conservative base, and Cruz certainly has that," added Wilson. "That said, the election isn't CPAC, and CPAC isn't the election."

Marco Rubio

Florida Sen. Marco Rubio is not the firebrand that Ted Cruz or even Rand Paul can be, and he doesn't have the some level of establishment support as someone like Jeb Bush. But he's young, articulate, and well-liked by a broad spectrum of conservative voters. He also speaks about foreign policy more fluently than many potential GOP candidates, thanks to his work on foreign affairs in the Senate. Expect him to try to solidify those strengths during his CPAC speech.

Luntz said Rubio "consistently does the best" of any potential GOP candidate in focus group dial testing. "In terms of simple messaging, Rubio's is the most positive of all the candidates," Luntz said. "He may appear young to some, but the more they hear from him, the more they like him."

Wilson predicted Rubio would "surprise the hell" out of the CPAC audience, despite his support for comprehensive immigration reform, which has earned him brickbats from conservatives.

"When people see Marco talking about his life story, his family history, his view of American exceptionalism, they're going to come out of their chairs," Wilson said. "They're going to be blown away. He's got a Reaganesque vision of optimism that I think will surprise some folks at CPAC who have only seen Marco Rubio in recent years through the filter of talk radio."

Rick Perry

During twelve-plus years as governor of Texas, Rick Perry amassed a conservative record that could serve him well in a GOP primary. But when he ran in 2012, his record took a backseat to his often unusual performance on the campaign trail, including a painful moment at one primary debate when he offered an "oops" after failing to remember the third federal department he'd proposed shuttering. If he hopes to succeed in 2016, he'll need to remind GOP voters about his record in Texas while assuaging any doubts sown by his ill-fated 2012 bid.

"Rick Perry is much more animated, much more passionate, and much more focused today than he was three years ago, and when people hear his record, they do give him a second look," said Luntz. "The question is whether he can erase perceptions of 2012 over the next year."

"Rick Perry has been born again hard," added Wilson. "He recognized what went off the rails in 2012, he's out telling the Texas story, and he needs to keep telling the Texas story. He needs to show the folks at CPAC that the Saturday Night Live cliché version of Rick Perry was an exception to his actual story."

Ben Carson

Carson, a retired neurosurgeon and conservative activist, burst onto the scene in 2013 by condemning Obamacare at the National Prayer Breakfast as the president looked on. He's earned a passionate core of disciples, some of whom have even set up an effort to draft him into the presidential race. But if he hopes to have a real shot at the GOP nomination in 2016, he'll need to broaden his focus, sharpen his message, and demonstrate the kind of political aptitude expected of a presidential candidate.

Some aren't sure he can rise to that level.

"I'm not convinced that he and his team are prepared to mount a serious national campaign," said Wilson. "There's a bit of rising concern that Ben Carson is a fundraising effort by a few consultants and not a national campaign."

"Ben Carson has to prove that he deserves more than just a second look," added Luntz. "He has to prove that someone who's never run before is worthy of a primary or caucus vote when there are so many other more qualified candidates."

Carly Fiorina

Former Hewlett-Packard CEO Carly Fiorina's last political foray - a 2010 California Senate bid - fell short. But she's earning some early buzz as a potential dark horse presidential candidate for the GOP in 2016. Hemminger, the ACU spokesman, tagged Fiorina as one to watch.

"Every campaign cycle, people are looking for something different," he said. "Her experience is so broad, and so vast, I really think she is that something special. I think you're going to see a lot more from her. I wouldn't be surprised to see a groundswell of support for her, particularly here at CPAC."

The fact that she's among the only women in the GOP's 2016 bullpen could help set her apart, but she will need to address concerns that someone with her nonpolitical background is prepared to carry a national party through a presidential election.

Luntz said Fiorina's business experience could be a selling point for her among conservatives, "but that alone isn't enough. She has to prove that someone without any political experience whatsoever not only knows the policies but also knows how to get elected."

"She's got some dark horse potential," Wilson added. "She needs to work on that and make sure people view her as someone who can play in the national space."