MIAMI — Republican Presidential hopeful Marco Rubio’s slow-go campaign strategy is puzzling party operatives in Iowa and New Hampshire, states where voters are used to candidates showering them with attention early and often.

While some GOP hopefuls are already highlighting their progress toward visiting all of Iowa’s 99 counties, Rubio’s return to the state this week marks his first stop in the caucus battleground in a month.

The Florida Senator hasn’t traveled to New Hampshire, home to the first-in-the-nation primary, since July 4, though he is expected to return before the end of August.

“You’ve had some of the others who have worked it a lot harder,” said Richard Schwarm, a former Iowa GOP Chairman who is uncommitted in the 2016 race. “I don’t think it’s too late. But I think he should step up the appearances here because we are wide open.”

Fergus Cullen, a former New Hampshire GOP Chairman who has yet to back a candidate, said that while Rubio benefits from “goodwill and interest,” his infrequent appearances in the state have cost him early endorsements.

“He would have more if he spent more time here,” Cullen said.

Rubio has visited New Hampshire just three times since announcing his campaign in early April. His stop in Iowa this week marks his fifth trip to the caucus state as a candidate.

The Senator’s advisers say they see little reason to worry about early state grumbling at this juncture in the campaign.

Even after a burst of momentum following his campaign launch and a strong performance in the first GOP debate, Rubio’s team has said it doesn’t expect the young senator to surge until fall or even winter, when voters start paying more attention to the White House race.

However, early polling shows Rubio has lost ground this summer while billionaire businessman-turned-Presidential candidate Donald Trump has surged, in part by tapping into the public’s anger with Washington.

Like some of his rivals, Rubio has spent much of the summer rounding up enough campaign cash to stay competitive in a lengthy primary.

Rubio’s campaign and outside groups supporting him raised a combined $45 million through the second quarter, a strong number but well below the massive haul from former Florida Gov. Jeb Bush, who brought in more than $100 million.

“We don’t expect to have the most money, but we will be competing in all 50 states,” said Alex Conant, the campaign’s spokesman.

Rubio, a first-term Senator, has also eschewed the campaign trail at times for hearings and votes on Capitol Hill, where he’s still taken heat for being absent often since launching his White House run in April.

He returned to Washington the day after his campaign launch for a vote on giving Congress a say on President Barack Obama’s Iran deal.

He also skipped an in-person appearance at a New Hampshire candidate forum earlier this month to vote on legislation to defund Planned Parenthood. He participated in the forum via video instead.

Rubio, a 44-year-old son of Cuban immigrants, is seen by some Republicans as a bright hope for a party desperate to attract younger, more diverse voters.

His optimistic, future-focused campaign message already has some Democrats worried that he would be a formidable general election opponent for front-runner Hillary Rodham Clinton.

“I think he’s a rising star in the Republican Party,” Iowa Gov. Terry Branstad said. “I think it would be worth his time to spend a significant amount of time in the state of Iowa.”

Some of Rubio’s rivals have devoted more time to the early voting states this summer.

Bush, who is counting on a strong performance in New Hampshire to propel his White House hopes, has made six trips to the state since announcing his campaign in mid-June. Ohio Gov. John Kasich has only officially been in the race for a month, but he has already matched Rubio’s travel to New Hampshire.

Of course, face time doesn’t always guarantee electoral success. Former Pennsylvania Sen. Rick Santorum turned his intense focus on Iowa into a surprise victory in the caucuses in 2012.

But his attempts to repeat that strategy four years later are showing little sign of success. Former Texas Gov. Rick Perry is also blanketing Iowa, but he has struggled in early polling.

Rubio was returning to Iowa this week for an appearance at the State Fair Aug. 18 and the opening of his campaign headquarters in Des Moines on Wednesday. Conant said Rubio would also make stops in New Hampshire, as well as South Carolina and Nevada, by the end of the month.

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By Julie Pace and Sergio Bustos. AP writer Catherine Lucey in Des Moines, Iowa, contributed