This story has been updated.

Thousands of conservatives gathered Thursday at the Conservative Political Action Conference to hear from potential Republican presidential contenders at an event that serves as an unofficial kick-off of the 2016 presidential race.

As a parade of party stars took the main stage, the crowd of activists cheered denunciations of President Obama and what one speaker called the “bad guys” on the political left.

“This is boot camp to take on the liberals!” said Rep. Marsha Blackburn (R-Tenn.) during her speech Thursday morning.

But at panel sessions -- and occasionally at the lectern at the Gaylord National Resort and Convention Center in snowy Prince George’s County -- there were more nuanced discussions about the need for Republicans to offer positive reforms on a range of issues, from criminal justice to health care.

That uneasy balance between vitriol for Democrats and a much-discussed desire to temper the party’s tone in order to expand the GOP’s political map in the coming presidential season was a running theme of the first day of what has become a four-day confab of politics and policy.

Maryland neurosurgeon Ben Carson, who spoke Thursday morning to start CPAC, said conservatives must do a better job of communicating their empathy to working voters, even as they resist supporting increased federal funding for some social programs.

“It is our responsibility to care for the indigent. It is not the government’s responsibility,” he said.

Speaking after Carson, Sen. Mike Lee (R-Utah) said conservatives should demand more than easy-to-digest rhetorical red meat from presidential candidates, or else risk rallying behind a subpar if charismatic nominee.

“We have a job to do, and it’s not to find a guy that shouts ‘freedom’ the loudest,” Lee said, hours before Sarah Palin appeared and a day before a speech by real-estate mogul Donald Trump- who said Wednesday he is serious about a presidential bid.

The jockeying among some of the more prominent Republican White House hopefuls defined the afternoon, with Wisconsin Gov. Scott Walker, Texas Sen. Ted Cruz and New Jersey Gov. Chris Christie among the candidates competing for conservative hearts.

Cruz chided congressional Republican leadership for “cutting a deal” on a bill on funding the Department of Homeland Security.

“Unfortunately Republican leadership is cutting a deal with Harry Reid and the Democrats to give in on executive amnesty," Cruz said. "...because they’re not listening to you."

Cruz spent much of his speech railing against Washington, urging the crowd to go for candidates who are willing to fight – not just against Democrats, but also against Republicans.

"Talk is cheap," he said, "Demand action, not talk."

Cruz likened himself to an iPhone app that upends the market, telling the crowd that he wants to be a “disruptive app” to politics.

Asked in a “lightning round” by Fox’s Sean Hannity to respond quickly to names. Bill Clinton: "Youth outreach." Barack Hussein Obama: "lawless impersonator."

Louisiana Gov. Bobby Jindal, like Cruz, took aim at both his fellow Republicans -- for failing to do enough to repeal President Obama's health-care law or stop Obama's plan to delay deportations for some young undocumented immigrants -- and at Obama himself.

"He has basically broken the Constitution. Broken the law," Jindal said of Obama. "It is time for our Republican leaders in congress to grow a spine. It’s time for them to do what we elected them to do."

Jindal also criticized Obama for not doing enough to confront the Islamic State terrorist group with military force. He said he rejected the State Department's argument that America could not "kill our way to victory," and argued ground troops might be necessary to win the fight.

"How have we ever won any war…if not killing our way to victory?" Jindal asked.

Sarah Palin's biggest applause line in an otherwise low-key speech came when she hit the Obama administration on its approach to combating the Islamic State.

"We can't kill our way out of war? Oh really? Tell that to the Nazis! Oh wait, you can't. They're dead. We killed them," she said.

Other candidates tried to play down their combative reputations. "Here are some of the words used to describe you: explosive; short-tempered; hot head; impatient; and that’s just what your friends are saying,” prodded conservative radio host Laura Ingraham, who led a question-and-answer session with Christie.

“Here’s the word they miss: Passionate,” Christie fired back. “I’m the son of a Sicilian mother and an Irish father, which means in my household I had to learn about dispute resolution really early.”

When Ingraham asked about an incident in which he told a reporter to “sit down and shut up,” the governor had a ready response: “Yeah well, sometimes people need to be told to sit down and shut up.”

The packed ballroom where the session was held erupted with applause.

Later in the day, calls of “run, Scott, run,” became a brief chant as Scott Walker found a warm reception from the crowd of rank-and-file Republicans and college students.

Walker turned his attention to a litany of issues that have long animated the Republican base: spending on social welfare programs, terrorism, Israel, and abortion. He knocked President Obama’s administration for not showing appropriate “respect” Israeli Prime Minister Benjamin Netanyahu, who plans to address Congress next week.

And he called “radical Islamic terrorism” a “threat to our way of life” -- and a threat he could confront, should he win the White House.

“If I can take on 100,000 protesters,” Walker said, referencing his fight against public-employee unions in his state, “I can do the same across the world.”

The most memorable moment perhaps came when Walker discussed the “right-to-work” legislation that is heading toward passage in Wisconsin’s state legislature. As Walker spoke, a protestor began to heckle Walker from the audience. Walker paused, looked toward the man and said, “Apparently protestors come from Wisconsin as well.”

CPAC goers, familiar with Walker’s battles against the unions in Wisconsin, rose to their feet in support. They clapped and hollered appreciatively as Walker pledged to not let his critics “drown out” the voices of “hard-working taxpayers.”

Still, it was underdog candidate Carly Fiorina who drew the day's first standing ovation with her critique of Hillary Clinton.

The former Hewlett-Packard CEO -- the only woman in the field of GOP candidates currently weighing a serious presidential bid -- set up a comparison between herself and the former secretary of state that she will likely carry forward as she continues weighing a 2016 run for the White House, highlighting her status as the only woman in the fledgling GOP presidential field.

“Mrs. Clinton, name an accomplishment. And in the meantime, please explain why we should accept that the millions and millions of dollars that have flowed into the Clinton Global Initiative from foreign governments doesn’t represent a conflict of interest,” Fiorina said.

Critics have seized on a report by The Washington Post that Clinton’s family foundation accepted donations from foreign governments while she was still serving as secretary of state.

Fiorina also took aim at Clinton’s tenure at the State Department.

“She tweets about women’s rights in this country and takes money from governments that deny women the most basic human rights,” she said. “She tweets about equal pay for women but won’t answer basic questions about her own office's pay standards — and neither will our president. Hillary likes hashtags. But she doesn’t know what leadership means.”

In fact, Clinton and another 2016 frontrunner -- former Florida governor Jeb Bush, who is slated to appear at CPAC Friday -- may not have been at the conference Thursday, but were never far from the spotlight.

New Jersey Gov. Chris Christie, fighting a bleed of establishment defections to Bush, took a swipe at the Republican frontrunner.

“If what happens is that the elites in Washington who make backroom deals deciding who the president is going to be, then [Bush] is the frontrunner," he told the CPAC crowd. "If the people of the United States decide to pick the President of the United States…[then] I’ll do okay if I run.”

So did Walker, subtly. Describing himself as the “son of a small-town preacher,” Walker touted his blue-collar roots and said he did not have a chance to visit Independence Hall in Philadelphia until he was an adult.

Without mentioning Bush by name, Walker presented a contrast with the son and brother of former presidents. “We didn’t have the money to go to historic sites,” Walker said, smiling tightly, as heads nodded understandingly throughout the room.

William Temple, 64, a tea-party activist from Georgia, said in an interview Thursday he would lead a walkout demonstration against Bush Friday by waving a Gadsden flag and sounding a call for conservatives to join him. Temple is well known attending national conservative meetings in revolutionary garb.

“We’re going to stand up, turn around, kick the dust off my feet, raise my flag, and walk out,” Temple said. “We’re going to have several hundred people, I don’t know how many more..... We’re going to make it clear to him that CPAC should not be inviting people who do not share our values.”

Temple’s efforts will be countered by longtime Bush loyalists, who are planning to travel in groups to CPAC early Friday to ensure the crowd is full of familiar faces. On Thursday, several Republican operatives shared an e-mail chain with The Washington Post that details Bush supporters’ organizing.

In between the headline speeches, CPAC was a showcase for scores of lesser-known conservative media figures and politicians who used their few minutes under the spotlights to introduce themselves to the people who they hope will become their fan base: small-dollar donors, students, and highly-engaged activists. Rep. Mia Love (R-Utah), 39, won favorable reviews during a morning panel where she poked fun at the Senate’s plodding nature and sounded optimistic about the GOP’s chances of winning over skeptics in 2016.

Attendees -- some of whom had never seen her before -- raved about Love, the first black Republican woman elected to Congress.

There was also reminiscing about the conservative movement’s past and its heroes, with many in the youthful crowd talking on stage and off about how they “got involved” or “turned right.” At a Thursday morning session, freshman Sen. Ben Sasse (R-Neb.), 43, spoke warmly of Ronald Reagan and when a video played soon after of former British Prime Minister Margaret Thatcher, a group of College Republicans clapped enthusiastically.

But throughout the day, presidential politics was inescapable, both in the main hall and beyond, as attendees began voting in the straw poll that will conclude CPAC this weekend

Politicking in the hallways was rampant aheadl. Michael Biundo, a New Hampshire strategist for Sen. Rand Paul (R-Ky.), huddled with attendees, hoping to help Paul build momentum among the libertarian conservatives at CPAC as the voting begins. Paul has previously won the straw poll twice, in 2013 and 2014.

He wasn't alone.

Ted Cruz's leadership PAC and supporters were constant presence, as the candidate made a push for a strong showing in this Saturday's straw poll.

Cruz, trailed by a Hollywood-style gaggle of people with cameras and microphones, spotted two young men dressed in stars and stripes boxer shorts, blazers and bow ties. They immediately called him over for a photo.

“That is quite a look,” Cruz said, eying the two young men. “You guys got only half-dressed.”

A woman in the scrum wasn’t pleased. “Put some pants on, we’re conservative,” she yelled.

“Sen. Cruz, will you sign my Constitution?” a young man asked the senator, who obliged.

And Ben Carson supporters were everywhere.

"I’m running for president – isn’t everyone?" joked GOP financier Foster Friess, who mingled with party leaders and presidential candidates backstage Thursday. "These presidential candidates are coming out of the wall, I’m telling you." Friess, however, said he resisting entreaties when hopefuls approach him in the green room: "I’m with Rick Santorum, 100.5 percent."

Still, should Santorum fail to win the GOP nomination in 2016, Friess said he is open to switching camps, and he will hear out anyone. To court him, Walker recently invited Friess to inaugural celebration. Friess said he admires Walker, Bush, and others in the field.

"Maybe we could get someone like Jeb if Santorum can’t make it," Friess said. "I’d go to the mat for practically all of them."

Update: A Walker spokeswoman responded Thursday evening to controversy surrounding the governor's comments about how the challenges he'd faced in his current role could compare to those he'd face in the Oval Office.

"Governor Walker believes our fight against ISIS is one of the most important issues our country faces," said Kirsten Kukowski in a statement. "He was in no way comparing any American citizen to ISIS. What the governor was saying was when faced with adversity he chooses strength and leadership. Those are the qualities we need to fix the leadership void this White House has created."

Katie Zezima, Jose DelReal, David Fahrenthold, Dan Balz, Abby Livingston, and Julie Percha contributed to this report.