The Republican presidential primary got going in earnest this month, but one of the Republican Party's biggest, most complex, most painful challenges still hasn't been solved: what to do about Univision.

The Spanish-language network has vast reach into America's Latino communities, a relentless focus on the Republican Party's least favorite issue, and close connections to Hillary Clinton. It's an immovable feature of the political landscape, and navigating around or through it is emerging as a key test for a party desperate to improve its dismal standing with a vital and growing share of the American electorate — and the subject of growing alarm among Republican leaders, operatives, and activists.

"It's highly questionable whether we're treated fairly on Univision," RNC chairman Reince Priebus told BuzzFeed News, adding that the party was going to keep at it. "You can fight all day long with people, not to say that that wouldn't continue, but at the same time you still have to get your message out."

Democrats see the dynamic just as clearly.

"The GOP needs Univision more than Univision needs the GOP," said Democratic pollster Fernand Amandi. "For a party looking to be competitive nationally again, they can't risk alienating the premier outlet that caters to the fastest-growing part of the electorate."

The scale of the Republicans' problem is hard to question. Univision reaches three times as many 18- to 49-year-old Hispanic adults with its flagship national news broadcast as CBS, NBC, and ABC do with their evening newscasts combined. The network reaches 96% of Hispanic households; 72% of Univision's primetime audience does not watch any of the top-rated English-language newscasts.

"After the Catholic Church, the next thing [American Latinos] trust the most is Univision," Univision News senior vice president Daniel Coronell told BuzzFeed News.

The network has a direct connection to the likely Democratic Party nominee for president. Univision's part-owner, Haim Saban, is one of Hillary Clinton's staunchest supporters. Of the former secretary of state, Saban once told an Israeli newspaper, "Seeing her in the White House is a big dream of mine." There are also formal connections: Univision partnered with the Clinton Foundation for an early education initiative in 2014.

Republicans, by and large, declined to criticize Univision on the record, citing its power. But speaking on the condition of anonymity, Republican operatives run down a litany of complaints, always returning to Univision's emphasis on immigration and the way the network's highest-profile journalist, Jorge Ramos, acts as an advocate on the issue.

"Immigration dictates their coverage," said a senior GOP source, a complaint made repeatedly to BuzzFeed News by Republicans. "We just took the Senate in Colorado, we just took the U.S. Senate, but Univision will generalize our platform as us not wanting to fund Obama's executive order," the source said of Republican opposition to the president's immigration actions.

The senior GOP source pointed to Colorado's first-ever Spanish-language debate, which was hosted by Univision in October, between Republican Mike Coffman and Democrat Andrew Romanoff. Immigration questions dominated the debate.

There have also been high-profile battles on other topics. In 2011, the network planned to report on the decades-old drug bust of Rubio's brother-in-law, but offered to approach on-air coverage of the story differently — if Rubio agreed to an interview with Ramos. The story aired and Rubio went on with Ramos the next year in an interview that became contentious over the issue.

It is the focus on immigration, in particular, that grates on Republicans, in part because they say it contrasts so sharply with what Univision executives tell them when they're asking for ad dollars. In the fall of 2013, less than a year after President Obama carried 71% of the Latino vote, for instance, Republican officials listened at the Capitol Hill Club to a presentation from two people: Keith Norman, a vice president from Univision, and an outside pollster for the network. The message was simple: Immigration, according to the polling, wasn't the top issue for Latinos. Jobs and the economy, education, and health care all ranked higher.

The pitch, the kind party officials had received before and received again in 2014, was clear — spend money with Univision to reach Latino voters in competitive congressional races in places like Florida, Arizona, Colorado, and Texas.

The Republican officials grumbled, then decided they had no choice, and bought digital ads on Univision.com and 30-second audio ads on Univision's music radio app Uforia in Miami, hitting the president on Obamacare.

Univision News' Coronell, a former high-profile journalist in Colombia, defended the network's coverage as fair, saying Republicans aren't the only ones complaining. He pointed to Ramos' sharp coverage of Obama's immigration record and their last sitdown interview as just the latest example of the Democratic administration's ongoing frustration with Univision.

"Some of the members of the White House communications team felt that Jorge was not respectful enough to the president and very insistent and picky with his questions," Coronell said. "Jorge Ramos asked about deportations numbers, he asked why he took so long to make this decision. The role of journalism is to ask, to be the counterweight to the politicians."

Coronell repeated a common refrain: The network has a standing invitation to top Republican officials. He downplayed the issue of Saban, the Clinton donor and Univision owner.

"With respect to Mr. Saban, Mr. Saban is not involved with editorial decisions at Univision," he said. "This is a serious company, he is very respectful to our journalistic independence. He's not connected with our day to day; we're not in this to build his happiness."

Univision representatives told BuzzFeed News the network's partnership with the Clinton Foundation also includes former Republican Sen. Bill Frist and Cindy McCain, the wife of Sen. John McCain, who are part of the Too Small to Fail leadership advisory council. (Former Florida Gov. Jeb Bush was approached for an education partnership, too, a Republican source said, but the talks never advanced.) The network also pointed to a Hispanic employment event it did with Gov. Chris Christie in New Jersey as evidence of broader political cooperation.