A protestor holds a sign as Republican presidential candidate Wisconsin Gov. Scott Walker speaks during a visit to the Iowa State Fair, Monday, Aug. 17, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) (Charlie Neibergall/AP)

Scott Walker has sought to reassure jittery donors and other supporters this week that he can turn around a swift decline in the polls in Iowa and elsewhere by going on the attack and emphasizing his conservatism on key issues.

In a conference call, one-on-one conversations and at a Tuesday lunch, the Wisconsin governor and favorite of anti-union conservatives told backers that his campaign is shifting to a more aggressive posture and will seek to tap into the anti-establishment fervor fueling the rise of Donald Trump and other outsider candidates.

During a conference call with top fundraisers Monday afternoon, Walker and his campaign manager were relatively candid in their assessment of the campaign’s shortcomings, according to notes of the conversation taken by a participant. Walker said the campaign will strive to do better in three areas: protest, passion and policy.

“We need to step it up and remind people that we didn’t just take on the unions and Democrats, we had to take on my own party establishment, those who did not want to take on the status quo,” Walker said on the call, according to the notes.

He added later: “One thing I heard about the first debate was: ‘You were fine, you did no wrong, but people want to feel the passion.’ ”

Republican presidential candidate Scott Walker unveiled a new health-care proposal that calls for repealing Obamacare. (Reuters)

The steps mark a clear shift for a candidate who has long positioned himself as a potential bridge between the party’s conservative and establishment wings. Walker now intends to focus his energy primarily on challengers from the right — a constituency that is particularly important in the first-in-the-nation Iowa caucuses, which aides consider a must-win contest for him.

Despite Walker’s strong and consistent start earlier this year, he has quickly lost ground in recent weeks and put in an underwhelming performance at the first GOP debate, on Aug 6. He went from double-digit standings in most national polls in July to single digits in several recent surveys. In the most recent poll of Iowa — where he has led for most of the summer — he was third behind Trump and tea party underdog Ben Carson, a retired neurosurgeon.

At the same time, Walker has veered to the right on abortion and other social issues, worrying some top backers. Stanley S. Hubbard, a conservative billionaire who oversees a Minnesota broadcasting company and has donated to Walker’s campaign, said the candidate has promised that he would not push a “social agenda” as president and is simply expressing his personal beliefs when asked.

“If he’s smart, he will get back to basics and get back to what he did in Wisconsin [and] get off the social issues,” said Hubbard, who had lunch on Tuesday with Walker and other campaign supporters. “No one is asking him to change the morals of America.”

Hubbard strongly opposes one immigration measure pushed by Trump this week: a call to stop giving citizenship to the children of illegal immigrants who are born in the United States. Walker said in an interview Monday that he would support ending birthright citizenship, then said other reforms might make that unnecessary.

Hubbard said that he “might really quickly change my allegiance” if Walker pushed for such a repeal, and that he “did not get a real straight answer” from the candidate at his Tuesday lunch. But Hubbard, who came away ready write more checks to help Walker, added: “I got the feeling that he is not at all anxious to talk about taking away those rights.”

Walker for months has pitched himself as a Washington outsider, but his candidacy has become overshadowed by non-politicians such as Trump, Carson and former Hewlett-Packard chief executive Carly Fiorina, who have connected with voters who are angry at those in office.

Republican presidential candidate, Wisconsin Gov. Scott Walker, center, holds a part in his hand as he tours Cass Screw Machine Products with company president Steve Wise, right, before presenting his health care plan, Tuesday, Aug. 18, 2015, in Brooklyn Center, Minn. (AP Photo/Jim Mone) (Jim Mone/AP)

Walker said on the conference call Monday that he wants to win over those voters, pitching himself as just as much of an outsider — but one with experience leading a state government.

“Instead of going after Trump, we need to go after his voters,” Walker said on the call. “True frustration — how we handle that is not by knocking him, but saying that we, too, share that frustration.”

Walker has in recent days adopted the rhetoric of the emerging outsider candidates along with some of their policy positions. Like Fiorina, Walker now says that he is frustrated that the Republican majorities in Washington have not delivered on their promises to voters. Walker said Monday that his immigration stances are “very similar” to those of Trump, who several months ago accused the Wisconsin governor of stealing his slogan “Make America great again.”

Walker also is trying to replicate the feisty anti-establishment tone Trump and others have shown on the campaign trail. The attempt was on full display on Monday morning when Walker spent 20 minutes on the political soapbox at the Iowa State Fair — a rite of passage for those dreaming of becoming president. The appearances regularly attract protesters, and Walker’s experience was no different.

There was shoving in the audience between Walker supporters and liberal activists. There was heckling and booing. Yellow signs popped up in the crowd reading: “Warning: Don’t let Scott Walker do to America what he did to Wisconsin.”

Walker regularly encounters detractors on the campaign trail and usually ignores them. But on Monday, he yelled at one protester in the crowd: “I’m not intimidated by you, sir, or anyone else out there. I will fight for the American people over and over and over and over again. You want someone who’s tested? I’m right here.”

The moment seemed out of character for a candidate who describes himself as “aggressively normal.” But the crowd loved it, and Twitter filled with praise from supporters.

Walker boasted about the interaction later that day during a stop in northern Iowa, although he exaggerated by saying that protesters were rushing the stage. On Tuesday afternoon, the campaign wrote in a mass fundraising e-mail that “the left wing special interests are back with even uglier attacks” against Walker, who “is not shaken easily.”

“People are upset, and they want to see some passion,” said Jonathan Burkan, a Walker fundraiser and financial services executive from New York who was on the Monday conference call. “That can be very positive. It’s important to show people that you can get fired up.”

Anthony Scaramucci, a New York investor and Walker fundraiser who also was on the call, said Walker and his team have quickly recognized that this contest will be much different than previous ones. The electorate is angry, and the campaign reflects that.

“A good candidate has to adapt to what’s going on,” Scaramucci said. “The candidate has to reflect the reality and the circumstances he’s in.”

Tom Hamburger contributed to this report.