An audience member at CPAC asked Wisconsin Gov. Scott Walker how he would respond to threats by militant groups such as the Islamic State if he were president. (AP)

Wisconsin Gov. Scott Walker, seeking to sustain his momentum in the early race for the 2016 GOP presidential nomination, made a muscular appeal Thursday to the party’s conservative base — touting his blue-collar roots and casting himself as a leader tough enough to take on the world’s biggest challenges.

Speaking to thousands of activists gathered for the opening day of the Conservative Political Action Conference, Walker said the commander in chief should “do everything in their power to ensure that the threat from radical Islamic terrorists does not wash up on American soil.”

“If I can take on 100,000 protesters,” Walker added, referring to his fight against labor unions in his state, “I can do the same across the world.”

That remark set off criticism, forcing Walker spokeswoman Kirsten Kukowski to issue a statement late Thursday saying that the governor “was in no way comparing any American citizen to [the Islamic State]. What the governor was saying was when faced with adversity he chooses strength and leadership.”

Walker was greeted by hearty applause and whoops — an enthusiasm for hawkish foreign policy positions that was evident in the crowd throughout the day.

The annual Conservative Political Action Conference is at the National Harbor, as conservative students and activists hear from 2016 hopefuls. Here’s a behind-the-scenes look at the sights and sounds of CPAC 2015. (Julie Percha/The Washington Post)

Walker was among a crop of likely presidential candidates who tested their messages on the gathering, taking shots at President Obama, presumed Democratic front-runner Hillary Rodham Clinton and each other.

Without mentioning former Florida governor Jeb Bush by name, for example, Walker offered himself as a contrast to the son and brother of former presidents, who is scheduled to speak Friday at the conference and has struggled to connect with some conservatives at this early stage in the race.

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.

“Our family didn’t have the money to go to some of the historic sites,” Walker said, smiling tightly.

Earlier in the day, New Jersey Gov. Chris Christie took pointed jabs at both Bush and Walker and signaled that he will double down on the freewheeling, pugilistic approach that propelled him onto the national stage.

When asked by radio host Laura Ingraham about an incident in which he told a heckler 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 erupted with applause.

He dismissed the gravitation of top party financiers to Bush, saying the former Florida governor was the pick of “the elites in Washington who make backroom deals.”

This year marks the sixth CPAC for William Temple, a tea party activist from Georgia. Dressed in 1770s German and Scottish war garb and waving a giant “Don’t Tread on Me” flag, Temple discusses his plans to lead a walk-out during former Gov. Jeb Bush’s speech on Friday. (Julie Percha/The Washington Post)

“If the people of the United States decide to pick the president of the United States . . . I’ll do okay if I run,” he said.

The New Jersey governor also took aim at the media, saying he is a target because he is unwilling to bend his views out of political expediency.

“So when you’re pro-life in 2009, you don’t cut a commercial four years later because the New York Times doesn’t like it,” Christie added in a veiled reference to Walker, who played down his anti-abortion views in a reelection ad last year. “Just because they write bad things about you doesn’t change your mind.”

The annual conference serves as a colorful convening of the party’s most conservative stalwarts. The National Rifle Association offered attendees a chance to win a Remington Model 783 bolt-action rifle. A woman from Rockwall, Tex., showcased a line of handbags with the Constitution printed on the lining. Two young men wearing boxer shorts festooned with stars and stripes called Sen. Ted Cruz (R-Tex.) over for a photo.

“This is boot camp to take on the liberals!” Rep. Marsha Blackburn (R-Tenn.) told the crowd.

But the conference serves perhaps more prominently as a testing ground for presidential hopefuls. And on Thursday, the halls of the Gaylord National Resort and Convention Center in snowy Prince George’s County were thick with likely White House contenders.

“I’m running for president — isn’t everyone?” joked GOP financier Foster Friess, who mingled backstage with party leaders and expected 2016 candidates.

The contours of the looming fight for the Republican presidential nomination took shape on stage throughout the day. Former Hewlett-Packard chief executive Carly Fiorina signaled the role she intends to play as a foil to Clinton.

In a sharply worded speech, Fiorina derided the former secretary of state as unaccomplished and pounced on new reports that the Clinton family foundation has accepted large sums from foreign governments.

“She tweets about women’s rights in this country and takes money from governments that deny women the most basic human rights,” said Fiorina, who drew large cheers and a standing ovation.

Cruz used his perch to chide the congressional Republican leadership for “cutting a deal” on a bill on funding the Department of Homeland Security, saying, “They are not listening to you.”

Louisiana Gov. Bobby Jindal also excoriated Republicans in Congress 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.

“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.”

He was followed by former Alaska governor Sarah Palin, who denounced Obama as a “lead-from-behind president” who missed the threat of 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,” Palin said.

For all the red meat thrown to the crowd, there were also nuanced discussions about the need for Republicans to offer positive reforms on a range of issues, from criminal justice to health care, underscoring the party’s attempt to expand the GOP’s political map in the coming presidential campaign season.

Maryland neurosurgeon Ben Carson, who kicked off the event with an early-morning speech, 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,” he said. “It is not the government’s responsibility.”

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.

Politicking in the hallways was rampant ahead of the straw poll that will conclude the CPAC conference. 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 won the straw poll in 2013 and 2014.

At a booth manned by staffers of Cruz’s leadership PAC, red plastic tailgate-party cups reading “Ted Cruz #makedclisten” were stacked in a triangle on a table, near temporary tattoos with the same slogan. The PAC staffers said they ordered about 500 T-shirts and were down to only about 100 by 11 a.m.

“He’s a strict constitutionalist,” said Donna Dawe of Fairfax, Va., who wore a large Ted Cruz sticker affixed to her shirt. “You can trust what he says. You can take it to the bank.”

David A. Fahrenthold and Katie Zezima contributed to this report.