Wisconsin governor and presidential candidate Scott Walker, shown here in in Woodbridge, Va., on Saturday, has plummeted in the polls after the rise of Donald Trump. EPA/JIM LO SCALZO (Jim Lo Scalzo/EPA)

Wisconsin Gov. Scott Walker surged into the top tier of the Republican presidential race with a fiery speech in the depths of winter in Iowa. But his candidacy has wilted in the heat of a summer dominated by Donald Trump, with loyalists and supporters now calling for an immediate mid-course correction.

Walker’s backers see a campaign discombobulated by Trump’s booming popularity and by his provocative language on immigration, China and other issues. They see in Walker a candidate who — in contrast to the discipline he showed in state races — continues to commit unforced errors, either out of lack of preparation or in an attempt to grab for part of the flamboyant businessman’s following.

These supporters say what is needed now is a return to basics, a more disciplined focus on the issues Walker long has championed in Wisconsin. They say there also needs to be a clear acknowledgment inside the campaign that the governor has yet to put to rest questions about his readiness to handle the problems and unexpected challenges that confront every president.

The newest Des Moines ­Register-Bloomberg Politics Iowa poll, released Saturday night, showed Walker’s support plummeting, underscoring the severity of the problems. Iowa is the linchpin of Walker’s early-state strategy, the place where he has been leading the polls for much of the year and where a victory has long been assumed among his senior staff.

Now, Walker is the favorite of just 8 percent among likely GOP caucusgoers, running third behind Trump (23 percent) and retired neurosurgeon Ben Carson (at 18 percent). The poll also showed, however, that Walker remains well liked by Iowa Republicans, with a favorability rating of 71 percent, second only to Carson.

Former Minnesota governor Tim Pawlenty, who unsuccessfully sought the GOP nomination four years ago, said in an interview that he sees both opportunities and challenges for Walker as he tries to regroup.

“He’s a hybrid candidate who can appeal to both base conservatives and not scare the establishment,” Pawlenty said. “So he’s in a good spot in terms of the potential territory he appeals to. But he’s still got to go out and rise to the occasion and close the sale.”

Instead of rising to the occasion, however, Walker has continued to raise doubts.

Several supporters say Walker appears to have had too many meetings with too many experts, turning him into a more timid version of himself. They miss the Midwestern candidate who focused on economic issues like weakening public unions, making painful cuts to the budget and reducing taxes by more than $2 billion.

A former Republican officeholder said Walker needs to project the political persona that first made him attractive to conservatives, rather than seemingly lurch further to the right on issues that never have been at his core.

“The Walker of the Iowa caucuses is not the Walker that people were used to seeing in Wisconsin,” said the Republican official, who spoke on the condition of anonymity in order to offer a candid view of Walker’s candidacy.

Walker said last week in North Carolina that he is “the same Scott Walker” he has always been and that any perceived shifts are exaggerations driven by the media. Although Walker once boasted about being a front-runner, he now says early polls are not a clear predictor of who will win the nomination months from now.

“These campaigns are marathons, not a sprint, and anyone who doubts Scott Walker this early in the race is making a big mistake,” said Michael Grebe, the chairman of Walker’s campaign, who served in the same role in all three of Walker’s gubernatorial races.

Even before the release of the Iowa poll, Republicans partial to Walker were expressing their worries about the direction of his campaign. “This has not been a good August,” said one of Walker’s top fundraisers, who asked for anonymity to candidly discuss problems within the campaign. “Something has to change.”

As Trump has continued to gain momentum, Walker’s campaign in the past two weeks launched a concerted effort to win over Trump’s supporters, many of them frustrated with traditional politicians. Even though Walker is a career officeholder who has spent most of his adult life campaigning, he has pitched himself as a Washington outsider who can use his political experience to get more accomplished from the White House.

As part of this reboot, Walker has adopted a more aggressive posture on the campaign trail, shouting back at protesters at the Iowa State Fair and sharpening his criticism of China, the media and members of his own party — even the Republicans back in Wisconsin who were instrumental to his rapid ascension.

Walker has also embraced several of Trump’s marquee stances, such as the businessman’s controversial proposal for reforming the immigration system, saying it’s similar to his own border plan. But Trump’s positions don’t always mesh with Walker’s style and experiences.

Walker struggled for more than a week to say whether he believes birthright citizenship, which is guaranteed by the 14th Amendment, should be repealed. As the financial markets tumbled last week in reaction to weaknesses in the Chinese economy, Walker called on President Obama to show “some backbone” and cancel the upcoming state visit of Chinese President Xi Jinping, with whom Walker met during a widely publicized 2013 trade mission.

While several candidates, including Trump, agreed that a state dinner is too much, they stopped short of fully disinviting the foreign leader. Walker later said communication and trade with China would continue, even if the ceremonial visit was canceled.

In discussing immigration on Sunday, Walker said constructing a wall on the U.S. border with Canada — the longest in the world at 5,525 miles — is “a legitimate issue for us to look at.”

Comments like this strike many Walker loyalists as too focused on chasing the hot issue of the day. Pawlenty highlighted another aspect of the challenge for Walker in what he called a “Trump-
Kardashian” world: Can an understated Midwesterner compete in a sometimes cartoonish environment?

“You don’t need to out-Trump Trump,” he said. “But in the modern era, where what you have is the fusion of entertaining and news and politics all balled together, you can’t just be a steady policy person. You can’t just be an entertainer either. You have to blend the two together.”

Walker loyalists say the first priority should be to help the governor rebalance himself as a candidate. That, they say, will require some tough love from his campaign advisers and more discipline in developing answers to questions about issues that are not central to Walker’s core message.

While a few of Walker’s campaign staffers have worked with him before, many are newcomers. Two of Walker’s former top political advisers, Keith Gilkes and Stephan Thompson, are now in charge of the pro-Walker super PAC that is legally separated from the campaign.

The campaign is led by Rick Wiley, a former Republican National Committee political director who grew up in the Midwest and has worked in Wisconsin before. Wiley is frequently on the trail with Walker, and several top supporters say he acts too much like a buddy and not enough like a chief operating officer.

“Every candidate needs somebody that can checkmate them in private, like a Karl Rove and ‘W,’ ” one top donor said, referring to George W. Bush’s longtime political adviser. “Is there some concern about senior experience around the governor, actual presidential experience? Yes, no question.”

Wiley, through a campaign spokeswoman, declined to respond to the comments. A spokeswoman said that while the campaign manager did spend the first full week of Walker’s campaign on the road and has made a few trips since then, he is usually at work in Madison.

Despite the falling poll numbers, Walker supporters are optimistic his campaign can still rebound — particularly if he performs well at the Sept. 16 debate at the Ronald Reagan Presidential Library.

“All campaigns go through cycles, and nobody has ridden all the way to victory,” said Gregory W. Slayton, a major Walker fundraiser who lives in New Hampshire. “There isn’t a candidate out there who hasn’t had really serious issues or challenges.”

Matea Gold and Robert Costa contributed to this report.